<PAGE>   1
     As filed with the Securities and Exchange Commission on April 2, 1999

                                                  Registration No. 333-________

================================================================================



                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D. C. 20549

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933


                      SECURITY DYNAMICS TECHNOLOGIES, INC.
             (Exact Name of Registrant as Specified in Its Charter)

             DELAWARE                                       04-2916506
  (State or Other Jurisdiction of                        (I.R.S. Employer
   Incorporation or Organization)                      Identification Number)

  36 CROSBY DRIVE, BEDFORD, MASSACHUSETTS                     01730
  (Address of Principal Executive Offices)                  (Zip Code)


           1998 NON-OFFICER EMPLOYEE STOCK INCENTIVE PLAN, AS AMENDED
                            (Full Title of the Plan)


                             ARTHUR W. COVIELLO, JR.
                      SECURITY DYNAMICS TECHNOLOGIES, INC.
                                 36 CROSBY DRIVE
                          BEDFORD, MASSACHUSETTS 01730
                     (Name and Address of Agent for Service)

                                 (781) 301-5000
          (Telephone Number, Including Area Code, of Agent for Service)



<PAGE>   2




                         CALCULATION OF REGISTRATION FEE
<TABLE>
==========================================================================================================
<CAPTION>
     Title of                               Proposed Maximum     Proposed Maximum
    Securities              Amount              Offering             Aggregate            Amount of
       to be                to be                Price                Offering           Registration
    Registered            Registered           Per Share               Price                 Fee
----------------------------------------------------------------------------------------------------------
<S>                       <C>                <C>                   <C>                  <C>
 Common Stock,            548,750              $16.875(1)            $9,260,157(1)          $2,575
 $.01 par value            shares             
==========================================================================================================

(1)  Estimated solely for the purpose of calculating the registration fee,
     and based on the average of the high and low prices of the Common
     Stock on the Nasdaq National Market on March 26, 1999 in accordance with 
     Rules 457(c) and 457(h) under the Securities Act of 1933.

==========================================================================================================
</TABLE>
<PAGE>   3
PART I.  INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

         The information required by Part I is included in documents sent or
given to participants in the Registrant's 1998 Non-Officer Employee Stock
Incentive Plan, as amended, pursuant to Rule 428(b)(1) of the Securities Act of
1933, as amended (the "Securities Act").

PART II. INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Statement of Incorporation by Reference

         Except as otherwise set forth below, this Registration Statement on
Form S-8 incorporates by reference the contents of the Registration Statement on
Form S-8, File No. 333-71075 (the "Initial Registration Statement"), filed by
the Registrant on January 25, 1999, relating to the Registrant's 1998
Non-Officer Employee Stock Incentive Plan.

         Item 5 of the Initial Registration Statement is amended and restated in
its entirety as follows:

         Item 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL

                  The legality of the Common Stock being offered hereby will be
passed upon for the Company by Hale and Dorr LLP, Boston, Massachusetts. A
senior partner of Hale and Dorr LLP beneficially owns approximately 3,300 shares
of the Registrant's Common Stock.





                                       1

<PAGE>   4


                                   SIGNATURES

     Pursuant to the requirements of the Securities Act, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the Town of Bedford, Massachusetts on April 2, 1999.
                                                             

                                        SECURITY DYNAMICS TECHNOLOGIES, INC.



                                        By:  /s/ Charles R. Stuckey, Jr.
                                             --------------------------------
                                             Charles R. Stuckey, Jr.
                                             Chairman of the Board and Chief
                                             Executive Officer



                                POWER OF ATTORNEY

     We, the undersigned officers and directors of Security Dynamics
Technologies, Inc. hereby severally constitute Charles R. Stuckey, Jr., Arthur
W. Coviello, Jr., Marian G. O'Leary and Hal J. Leibowitz, and each of them
singly, our true and lawful attorneys with full power to them, and each of them
singly, to sign for us and in our names in the capacities indicated below, the
Registration Statement on Form S-8 filed herewith and any and all subsequent
amendments to said Registration Statement, and generally to do all such things
in our names and behalf in our capacities as officers and directors to enable
Security Dynamics Technologies, Inc. to comply with all requirements of the
Securities and Exchange Commission, hereby ratifying and confirming our
signatures as they may be signed by said attorneys, or any of them, to said
Registration Statement and any and all amendments thereto.

                                       2

<PAGE>   5


     Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated.


     Signature                           Title                         Date
     ---------                           -----                         ----

/s/ Charles R. Stuckey, Jr.    Chairman of the Board of           April 2, 1999
----------------------------   Directors and Chief     
Charles R. Stuckey, Jr.        Executive Officer (Principal
                               Executive Officer)

/s/ Marian G. O'Leary          Senior Vice President, Finance,    April 2, 1999
----------------------------   Chief Financial Officer and
Marian G. O'Leary              Treasurer (Principal Financial
                               and Accounting Officer)

/s/ D. James Bidzos            Director                           April 2, 1999
----------------------------
D. James Bidzos


                               Director                           
----------------------------
Richard L. Earnest


/s/ Joseph B. Lassiter, III    Director                           April 2, 1999
----------------------------
Joseph B. Lassiter, III


/s/ George M. Middlemas        Director                           April 2, 1999
----------------------------
George M. Middlemas


/s/ James K. Sims              Director                           April 2, 1999
----------------------------
James K. Sims


                               Director                           
----------------------------
Taher Elgamal


                               Director                           
----------------------------
Arthur W. Coviello, Jr.



                                       3

<PAGE>   6


                                  EXHIBIT INDEX


Exhibit
Number                        Description
-------                       -----------

   4.1         Specimen Certificate of Common Stock, $.01 par value per share,
               of the Registrant is incorporated herein by reference to Exhibit
               4.1 to the Registrant's Registration Statement on Form S-1, as
               amended (File No. 33-85606)

   5           Opinion of Hale and Dorr LLP

  23.1         Consent of Hale and Dorr LLP (included in Exhibit 5)

  23.2         Consent of Deloitte & Touche LLP, independent auditors

  24           Power of Attorney (included in the signature pages of this
               Registration Statement)

                                       4
[{"type": "S-8", "sequence": "1", "description": "SECURITY DYNAMICS", "secsgml_size_bytes": 8711}]
{"company-data": {"conformed-name": "SECURITY DYNAMICS TECHNOLOGIES INC /DE/", "cik": "0000932064", "assigned-sic": "3577", "irs-number": "042916506", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-75569", "film-number": "99586417"}, "business-address": {"street1": "36 CROSBY DRIVE", "city": "BEDFORD", "state": "MA", "zip": "01730", "phone": "6176877000"}, "mail-address": {"street1": "36 CROSBY DRIVE", "city": "BEDFORD", "state": "MA", "zip": "01730"}}
1
     As filed with the Securities and Exchange Commission on April 2, 1999

                                                  Registration No. 333-________

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D. C. 20549

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                      SECURITY DYNAMICS TECHNOLOGIES, INC.
             (Exact Name of Registrant as Specified in Its Charter)

             DELAWARE                                       04-2916506
  (State or Other Jurisdiction of                        (I.R.S. Employer
   Incorporation or Organization)                      Identification Number)

  36 CROSBY DRIVE, BEDFORD, MASSACHUSETTS                     01730
  (Address of Principal Executive Offices)                  (Zip Code)

           1998 NON-OFFICER EMPLOYEE STOCK INCENTIVE PLAN, AS AMENDED
                            (Full Title of the Plan)

                             ARTHUR W. COVIELLO, JR.
                      SECURITY DYNAMICS TECHNOLOGIES, INC.
                                 36 CROSBY DRIVE
                          BEDFORD, MASSACHUSETTS 01730
                     (Name and Address of Agent for Service)

                                 (781) 301-5000
          (Telephone Number, Including Area Code, of Agent for Service)
2

                         CALCULATION OF REGISTRATION FEE

==========================================================================================================
Title of                               Proposed Maximum     Proposed Maximum
    Securities              Amount              Offering             Aggregate            Amount of
       to be                to be                Price                Offering           Registration
    Registered            Registered           Per Share               Price                 Fee
----------------------------------------------------------------------------------------------------------
Common Stock,            548,750              $16.875(1)            $9,260,157(1)          $2,575
 $.01 par value            shares             
==========================================================================================================

(1)  Estimated solely for the purpose of calculating the registration fee,
     and based on the average of the high and low prices of the Common
     Stock on the Nasdaq National Market on March 26, 1999 in accordance with 
     Rules 457(c) and 457(h) under the Securities Act of 1933.

==========================================================================================================
3
PART I.  INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

         The information required by Part I is included in documents sent or
given to participants in the Registrant's 1998 Non-Officer Employee Stock
Incentive Plan, as amended, pursuant to Rule 428(b)(1) of the Securities Act of
1933, as amended (the "Securities Act").

PART II. INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Statement of Incorporation by Reference

         Except as otherwise set forth below, this Registration Statement on
Form S-8 incorporates by reference the contents of the Registration Statement on
Form S-8, File No. 333-71075 (the "Initial Registration Statement"), filed by
the Registrant on January 25, 1999, relating to the Registrant's 1998
Non-Officer Employee Stock Incentive Plan.

         Item 5 of the Initial Registration Statement is amended and restated in
its entirety as follows:

         Item 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL

                  The legality of the Common Stock being offered hereby will be
passed upon for the Company by Hale and Dorr LLP, Boston, Massachusetts. A
senior partner of Hale and Dorr LLP beneficially owns approximately 3,300 shares
of the Registrant's Common Stock.

                                       1
4

                                   SIGNATURES

     Pursuant to the requirements of the Securities Act, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the Town of Bedford, Massachusetts on April 2, 1999.
                                                             

                                        SECURITY DYNAMICS TECHNOLOGIES, INC.

                                        By:  /s/ Charles R. Stuckey, Jr.
                                             --------------------------------
                                             Charles R. Stuckey, Jr.
                                             Chairman of the Board and Chief
                                             Executive Officer

                                POWER OF ATTORNEY

     We, the undersigned officers and directors of Security Dynamics
Technologies, Inc. hereby severally constitute Charles R. Stuckey, Jr., Arthur
W. Coviello, Jr., Marian G. O'Leary and Hal J. Leibowitz, and each of them
singly, our true and lawful attorneys with full power to them, and each of them
singly, to sign for us and in our names in the capacities indicated below, the
Registration Statement on Form S-8 filed herewith and any and all subsequent
amendments to said Registration Statement, and generally to do all such things
in our names and behalf in our capacities as officers and directors to enable
Security Dynamics Technologies, Inc. to comply with all requirements of the
Securities and Exchange Commission, hereby ratifying and confirming our
signatures as they may be signed by said attorneys, or any of them, to said
Registration Statement and any and all amendments thereto.

                                       2
5

     Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated.

     Signature                           Title                         Date
     ---------                           -----                         ----

/s/ Charles R. Stuckey, Jr.    Chairman of the Board of           April 2, 1999
----------------------------   Directors and Chief     
Charles R. Stuckey, Jr.        Executive Officer (Principal
                               Executive Officer)

/s/ Marian G. O'Leary          Senior Vice President, Finance,    April 2, 1999
----------------------------   Chief Financial Officer and
Marian G. O'Leary              Treasurer (Principal Financial
                               and Accounting Officer)

/s/ D. James Bidzos            Director                           April 2, 1999
----------------------------
D. James Bidzos

                               Director                           
----------------------------
Richard L. Earnest

/s/ Joseph B. Lassiter, III    Director                           April 2, 1999
----------------------------
Joseph B. Lassiter, III

/s/ George M. Middlemas        Director                           April 2, 1999
----------------------------
George M. Middlemas

/s/ James K. Sims              Director                           April 2, 1999
----------------------------
James K. Sims

                               Director                           
----------------------------
Taher Elgamal

                               Director                           
----------------------------
Arthur W. Coviello, Jr.

                                       3
6

                                  EXHIBIT INDEX

Exhibit
Number                        Description
-------                       -----------

   4.1         Specimen Certificate of Common Stock, $.01 par value per share,
               of the Registrant is incorporated herein by reference to Exhibit
               4.1 to the Registrant's Registration Statement on Form S-1, as
               amended (File No. 33-85606)

   5           Opinion of Hale and Dorr LLP

  23.1         Consent of Hale and Dorr LLP (included in Exhibit 5)

  23.2         Consent of Deloitte & Touche LLP, independent auditors

  24           Power of Attorney (included in the signature pages of this
               Registration Statement)

                                       4