<PAGE>   1
    As filed with the Securities and Exchange Commission on December 15, 2000
                                                       Registration No. 333-____
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                           -------------------------

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                           -------------------------

                                  CYSIVE, INC.
             (Exact Name of Registrant as Specified in Its Charter)

<TABLE>
<S>                                                       <C>
            DELAWARE                                             54-1698017
(State or Other Jurisdiction of                                (IRS Employer
 Incorporation or Organization)                              Identification No.)
</TABLE>

                        10780 PARKRIDGE BLVD., SUITE 400
                                RESTON, VA 20191
               (Address of Principal Executive Offices) (Zip Code)

                           -------------------------

         CYSIVE, INC. SECOND AMENDED AND RESTATED 1994 STOCK OPTION PLAN
                            (Full Title of the Plan)

                           -------------------------

                            NELSON A. CARBONELL, JR.
                 CHAIRMAN, PRESIDENT AND CHIEF EXECUTIVE OFFICER
                                  CYSIVE, INC.
                        10780 PARKRIDGE BLVD., SUITE 400
                                RESTON, VA 20191
                     (Name and Address of Agent for Service)


                                 (703) 259-2300
          (Telephone Number, Including Area Code, of Agent for Service)

                                 With a Copy to:

                              PAUL V. ROGERS, ESQ.
                               COVINGTON & BURLING
                         1201 PENNSYLVANIA AVENUE, N.W.
                              WASHINGTON, DC 20004
                                 (202) 662-6000


                           -------------------------
<TABLE>
<CAPTION>
                                   CALCULATION OF REGISTRATION FEE
===================================================================================================
                                              Proposed
 Title of Each Class of                   Maximum Offering        Proposed
    Securities to be       Amount to be    Price Per Share   Maximum Aggregate      Amount of
       Registered         Registered (1)         (2)         Offering Price (2)  Registration Fee
---------------------------------------------------------------------------------------------------
<S>                       <C>             <C>                <C>                 <C>
Common Stock, par value
       $0.01 per
   share.............     121,350 shares        $4.56             $553,356             $146
===================================================================================================
</TABLE>

(1) Pursuant to Rule 416(a) under the Securities Act of 1933, as amended (the
    "Securities Act"), the number of shares of Common Stock registered hereby is
    subject to adjustment to prevent dilution by reason of any stock dividend,
    stock split, recapitalization or other similar transaction.
(2) Calculated in accordance with Rule 457(h) under the Securities Act on the
    basis of the average of the high and low sales prices per share of Common
    Stock on December 13, 2000, as reported by the Nasdaq National Market.

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



<PAGE>   2


                     STATEMENT OF INCORPORATION BY REFERENCE

        The Registrant hereby incorporates by reference into this registration
statement the Registrant's Registration Statement on Form S-8 (File No.
333-42834).


                                   SIGNATURES

               Pursuant to the requirements of the Securities Act of 1933, 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 City of Reston, Commonwealth of Virginia, on this 15th day of
December, 2000.

                                  CYSIVE, INC.


                                  By: /s/ Nelson A. Carbonell, Jr.
                                      -----------------------------
                                      Nelson A. Carbonell, Jr.
                                      Chairman of the Board, President and Chief
                                      Executive Officer


                                POWER OF ATTORNEY

               Each person whose signature appears below under the heading
"Signature" constitutes and appoints Nelson A. Carbonell, Jr. and John R. Lund,
or any of them, his true and lawful attorney-in-fact and agent with full power
of substitution and resubstitution, for him and in his name, place and stead, in
any and all capacities to sign any or all Registration Statements on Form S-8
with respect to any securities to be offered and issued by Cysive, Inc., a
Delaware corporation (the "Registrant"), pursuant to any employee benefit plan
(as such term is defined in the General Instructions to Form S-8) of the
Registrant and any or all amendments to any such Registration Statement, and to
file the same, with all exhibits thereto, and other documents in connection
therewith, granting unto said attorneys-in-fact and agents, each acting alone,
full power and authority to do and perform each and every act and thing
requisite and necessary to be done in and about the premises, as fully for all
intents and purposes as he might or could do in person, hereby ratifying and
confirming all that said attorneys-in-fact and agents, each acting alone, or his
substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

               Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed on the 15th day of December, 2000, by the
following persons in the capacities indicated.


<TABLE>
<CAPTION>
           Signature                                Title                           Date
           ---------                                -----                           ----

<S>                               <C>                                           <C>
  /s/ Nelson A. Carbonell, Jr.    Chairman of the Board, President and          December 15, 2000
-------------------------------   Chief Executive Officer (principal
    Nelson A. Carbonell, Jr.      executive officer)


        /s/ John R. Lund          Vice President, Chief Financial Officer,      December 15, 2000
-------------------------------   Treasurer, Secretary and Director
          John R. Lund            (principal financial and accounting
                                  officer)


        /s/ Jon S. Korin          Director                                      December 15, 2000
-------------------------------
          Jon S. Korin


       /s/ John M. Sabin          Director                                      December 15, 2000
-------------------------------
         John M. Sabin
</TABLE>


<PAGE>   3

                                  EXHIBIT INDEX


<TABLE>
<CAPTION>
  Exhibit No.                Description
  -----------                -----------
<S>            <C>
      4.1      Amended and Restated Certificate of Incorporation of the Registrant (1)
      4.2      Amended and Restated Bylaws of the Registrant (1)
      5.1      Opinion of Joseph M. Boyle, Esq. (3)
      23.1     Consent of Ernst & Young LLP (3)
      23.2     Consent of Joseph M. Boyle, Esq. (included in Exhibit 5.1)
      24.1     Power of Attorney (included on signature page)
      99.1     Cysive, Inc. Second Amended and Restated 1994 Stock Option Plan (2)
</TABLE>


----------------------
      (1)   Incorporated by reference to the Registrant's Registration
            Statement on Form S-1 (File No. 333-85651).

      (2)   Incorporated by reference to the Registrant's Definitive Proxy
            Statement on Form DEF 14A (File No. 000-27607).

      (3)   Filed herewith
[{"type": "S-8", "sequence": "1", "filename": "w43551s-8.txt", "description": "REGISTRATION STATEMENT", "secsgml_size_bytes": 8545}]
{"company-data": {"conformed-name": "CYSIVE INC", "cik": "0001093193", "assigned-sic": "7371", "irs-number": "541698017", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-51910", "film-number": "789975"}, "business-address": {"street1": "10780 PARKRIDGE BLVD", "street2": "STE 400", "city": "RESTON", "state": "VA", "zip": "20191", "phone": "7032592300"}, "mail-address": {"street1": "10780 PARKRIDGE BLVD", "street2": "STE 400", "city": "RESTON", "state": "VA", "zip": "20191"}}
1
    As filed with the Securities and Exchange Commission on December 15, 2000
                                                       Registration No. 333-____
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                           -------------------------

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                           -------------------------

                                  CYSIVE, INC.
             (Exact Name of Registrant as Specified in Its Charter)
DELAWARE                                             54-1698017
(State or Other Jurisdiction of                                (IRS Employer
 Incorporation or Organization)                              Identification No.)
10780 PARKRIDGE BLVD., SUITE 400
                                RESTON, VA 20191
               (Address of Principal Executive Offices) (Zip Code)

                           -------------------------

         CYSIVE, INC. SECOND AMENDED AND RESTATED 1994 STOCK OPTION PLAN
                            (Full Title of the Plan)

                           -------------------------

                            NELSON A. CARBONELL, JR.
                 CHAIRMAN, PRESIDENT AND CHIEF EXECUTIVE OFFICER
                                  CYSIVE, INC.
                        10780 PARKRIDGE BLVD., SUITE 400
                                RESTON, VA 20191
                     (Name and Address of Agent for Service)

                                 (703) 259-2300
          (Telephone Number, Including Area Code, of Agent for Service)

                                 With a Copy to:

                              PAUL V. ROGERS, ESQ.
                               COVINGTON & BURLING
                         1201 PENNSYLVANIA AVENUE, N.W.
                              WASHINGTON, DC 20004
                                 (202) 662-6000

                           -------------------------
CALCULATION OF REGISTRATION FEE
===================================================================================================
                                              Proposed
 Title of Each Class of                   Maximum Offering        Proposed
    Securities to be       Amount to be    Price Per Share   Maximum Aggregate      Amount of
       Registered         Registered (1)         (2)         Offering Price (2)  Registration Fee
---------------------------------------------------------------------------------------------------
Common Stock, par value
       $0.01 per
   share.............     121,350 shares        $4.56             $553,356             $146
===================================================================================================
(1) Pursuant to Rule 416(a) under the Securities Act of 1933, as amended (the
    "Securities Act"), the number of shares of Common Stock registered hereby is
    subject to adjustment to prevent dilution by reason of any stock dividend,
    stock split, recapitalization or other similar transaction.
(2) Calculated in accordance with Rule 457(h) under the Securities Act on the
    basis of the average of the high and low sales prices per share of Common
    Stock on December 13, 2000, as reported by the Nasdaq National Market.

================================================================================
2

                     STATEMENT OF INCORPORATION BY REFERENCE

        The Registrant hereby incorporates by reference into this registration
statement the Registrant's Registration Statement on Form S-8 (File No.
333-42834).

                                   SIGNATURES

               Pursuant to the requirements of the Securities Act of 1933, 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 City of Reston, Commonwealth of Virginia, on this 15th day of
December, 2000.

                                  CYSIVE, INC.

                                  By: /s/ Nelson A. Carbonell, Jr.
                                      -----------------------------
                                      Nelson A. Carbonell, Jr.
                                      Chairman of the Board, President and Chief
                                      Executive Officer

                                POWER OF ATTORNEY

               Each person whose signature appears below under the heading
"Signature" constitutes and appoints Nelson A. Carbonell, Jr. and John R. Lund,
or any of them, his true and lawful attorney-in-fact and agent with full power
of substitution and resubstitution, for him and in his name, place and stead, in
any and all capacities to sign any or all Registration Statements on Form S-8
with respect to any securities to be offered and issued by Cysive, Inc., a
Delaware corporation (the "Registrant"), pursuant to any employee benefit plan
(as such term is defined in the General Instructions to Form S-8) of the
Registrant and any or all amendments to any such Registration Statement, and to
file the same, with all exhibits thereto, and other documents in connection
therewith, granting unto said attorneys-in-fact and agents, each acting alone,
full power and authority to do and perform each and every act and thing
requisite and necessary to be done in and about the premises, as fully for all
intents and purposes as he might or could do in person, hereby ratifying and
confirming all that said attorneys-in-fact and agents, each acting alone, or his
substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

               Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed on the 15th day of December, 2000, by the
following persons in the capacities indicated.
Signature                                Title                           Date
           ---------                                -----                           ----
/s/ Nelson A. Carbonell, Jr.    Chairman of the Board, President and          December 15, 2000
-------------------------------   Chief Executive Officer (principal
    Nelson A. Carbonell, Jr.      executive officer)

        /s/ John R. Lund          Vice President, Chief Financial Officer,      December 15, 2000
-------------------------------   Treasurer, Secretary and Director
          John R. Lund            (principal financial and accounting
                                  officer)

        /s/ Jon S. Korin          Director                                      December 15, 2000
-------------------------------
          Jon S. Korin

       /s/ John M. Sabin          Director                                      December 15, 2000
-------------------------------
         John M. Sabin
3

                                  EXHIBIT INDEX
Exhibit No.                Description
  -----------                -----------
4.1      Amended and Restated Certificate of Incorporation of the Registrant (1)
      4.2      Amended and Restated Bylaws of the Registrant (1)
      5.1      Opinion of Joseph M. Boyle, Esq. (3)
      23.1     Consent of Ernst & Young LLP (3)
      23.2     Consent of Joseph M. Boyle, Esq. (included in Exhibit 5.1)
      24.1     Power of Attorney (included on signature page)
      99.1     Cysive, Inc. Second Amended and Restated 1994 Stock Option Plan (2)
----------------------
      (1)   Incorporated by reference to the Registrant's Registration
            Statement on Form S-1 (File No. 333-85651).

      (2)   Incorporated by reference to the Registrant's Definitive Proxy
            Statement on Form DEF 14A (File No. 000-27607).

      (3)   Filed herewith