<PAGE>
                                                                    EXHIBIT 10.2

[BANK OF AMERICA LOGO APPEARS HERE]

                                 Promissory Note
                                                             Customer# 41-567249

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<S>                          <C>            <C>                      <C>
Date June 10, 2002 []New     [X]Renewal     Amount $10,000,000.00    Maturity Date June 10, 2004
     -------------                                 --------------                  -------------

================================================================================================
Bank:                                            Borrower:

Bank of America, N.A.
Banking Center:                                       OPNET Technologies, Inc.
                                                      7255 Woodmont Avenue, Suite 250
     Commercial Banking                               Bethesda, Maryland 20814
     6610 Rockledge Drive
     Bethesda, Maryland 20817-1811

     County:  Montgomery                              County: Montgomery

================================================================================================
</TABLE>

FOR VALUE RECEIVED, the undersigned Borrower unconditionally (and jointly and
severally, if more than one) promises to pay to the order of Bank, its
successors and assigns, without setoff, at its offices indicated at the
beginning of this Note, or at such other place as may be designated by Bank, the
principal amount of Ten Million and 00/100 Dollars ($10,000,000.00), or so much
thereof as may be advanced from time to time in immediately available funds,
together with interest computed daily on the outstanding principal balance
hereunder, at an annual interest rate, and in accordance with the payment
schedule, indicated below.

[This Note contains some provisions preceded by boxes. If a box is marked, the
provision applies to this transaction; if it is not marked, the provision does
not apply to this transaction.]

1. Rate.

See Attached Exhibit "A"

Notwithstanding any provision of this Note, Bank does not intend to charge and
Borrower shall not be required to pay any amount of interest or other charges in
excess of the maximum permitted by the applicable law of the State of Maryland;
if any higher rate ceiling is lawful, then that higher rate ceiling shall apply.
Any payment in excess of such maximum shall be refunded to Borrower or credited
against principal, at the option of Bank.

2. Accrual Method. Unless otherwise indicated, interest at the Rate set forth
above will be calculated by the 365/360 day method (a daily amount of interest
is computed for a hypothetical year of 360 days; that amount is multiplied by
the actual number of days for which any principal is outstanding hereunder). If
interest is not to be computed using this method, the method shall be: N/A.
                                                                       ---

3. Rate Change Date. Any Rate based on a fluctuating index or base rate will
change, unless otherwise provided, each time and as of the date that the index
or base rate changes. If the Rate is to change on any other date or at any other
interval, the change shall be: N/A. In the event any index is discontinued, Bank
                               ---
shall substitute an index determined by Bank to be comparable, in its sole
discretion.

4. Payment Schedule. All payments received hereunder shall be applied first to
the payment of any expense or charges payable hereunder or under any other loan
documents executed in connection with this Note, then to interest due and
payable, with the balance applied to principal, or in such other order as Bank
shall determine at its option.

Single Principal Payment. Principal shall be paid in full in a single payment on
June 10, 2004. Interest thereon shall be paid monthly, commencing on July 10,
2002, and continuing on the same day of each successive month, quarter or other
period (as applicable) thereafter, with a final payment of all unpaid interest
at the stated maturity of this Note.

5. Revolving Feature.

[X] Borrower may borrow, repay and reborrow hereunder at any time, up to a
maximum aggregate amount outstanding at any one time equal to the principal
amount of this Note, provided, that Borrower is not in default under any
provision of this Note, any other documents executed in connection with this
Note, or any other note or other loan documents now or hereafter executed in
connection with any other obligation of Borrower to Bank, and provided that the
borrowings hereunder do not exceed any borrowing base or other limitation on
borrowings by Borrower. Bank shall incur no liability for its refusal to advance
funds based upon its determination that any conditions of such further advances
have not been met. Bank records of the amounts borrowed from time to time shall
be conclusive proof thereof.

     [] Uncommitted Facility. Borrower acknowledges and agrees that,
     notwithstanding any provisions of this Note or any other documents executed
     in connection with this Note, Bank has no obligation to make any advance,
     and that all advances are at the sole discretion of Bank.

     [] Out-Of-Debt Period. For a period of at least __ consecutive days during
     [] each fiscal year, [] any consecutive 12-month period, Borrower shall
     fully pay down the balance of this Note, so that no amount of principal or
     interest and no other obligation under this Note remains outstanding.

6.   Automatic Payment.

[ ] Borrower has elected to authorize Bank to effect payment of sums due under
this Note by means of debiting Borrower's account number ______________________.
This authorization shall not affect the obligation of Borrower to pay such sums
when due, without notice, if there are insufficient funds in such account to
make such payment in full on the due date thereof, or if Bank fails to debit the
account.

                                       1

                                                              Approved: 09-21-95
                                                               Revised: 08-30-99

<PAGE>

7. Waivers, Consents and Covenants. Borrower, any endorser, or guarantor hereof
or any other party hereto (individually an "Obligor" and collectively
"Obligors") and each of them jointly and severally: (a) waive presentment,
demand, protest, notice of demand, notice of intent to accelerate, notice of
acceleration of maturity, notice of protest, notice of nonpayment, notice of
dishonor, and any other notice required to be given under the law to any Obligor
in connection with the delivery, acceptance, performance, default or enforcement
of this Note, any endorsement or guaranty of this Note, or any other documents
executed in connection with this Note or any other note or other loan documents
now or hereafter executed in connection with any obligation of Borrower to Bank
(the "Loan Documents"); (b) consent to all delays, extensions, renewals or other
modifications of this Note or the Loan Documents, or waivers of any term hereof
or of the Loan Documents, or release or discharge by Bank of any of Obligors, or
release, substitution or exchange of any security for the payment hereof, or the
failure to act on the part of Bank, or any indulgence shown by Bank (without
notice to or further assent from any of Obligors), and agree that no such
action, failure to act or failure to exercise any right or remedy by Bank shall
in any way affect or impair the obligations of any Obligors or be construed as a
waiver by Bank of, or otherwise affect, any of Bank's rights under this Note,
under any endorsement or guaranty of this Note or under any of the Loan
Documents; and (c) agree to pay, on demand, all costs and expenses of collection
or defense of this Note or of any endorsement or guaranty hereof and/or the
enforcement or defense of Bank's rights with respect to, or the administration,
supervision, preservation, protection of, or realization upon, any property
securing payment hereof, including, without limitation, reasonable attorney's
fees, including fees related to any suit, mediation or arbitration proceeding,
out of court payment agreement, trial, appeal, bankruptcy proceedings or other
proceeding, in the amount of 10% of the principal amount of this Note, or such
greater amount as may be determined reasonable by any arbitrator or court,
whichever is applicable.

8. Prepayments. Prepayments may be made in whole or in part at any time on any
loan for which the Rate is based on the Prime Rate or on any other fluctuating
Rate or index which may change daily. All prepayments of principal shall be
applied in the inverse order of maturity, or in such other order as Bank shall
determine in its sole discretion.

9. Delinquency Charge. To the extent permitted by law, a delinquency charge may
be imposed in an amount not to exceed four percent (4%) of any payment that is
more than fifteen days late.

10. Events of Default. The following are events of default hereunder: (a) the
failure to pay or perform any obligation, liability or indebtedness of any
Obligor to Bank, or to any affiliate or subsidiary of Bank of America
Corporation, whether under this Note or any Loan Documents, as and when due
(whether upon demand, at maturity or by acceleration) and not remedied or cured
as permitted in Section 6 under the Loan Agreement dated June 10, 2002; (b) the
failure to pay or perform any other obligation, liability or indebtedness of any
Obligor in excess of $1,000,000.00 to any other party; (c) the death of any
Obligor (if an individual); (d) the resignation or withdrawal of any material
owner/Guarantor of Borrower, as determined by Bank in its sole discretion; (e)
the commencement of a proceeding against any Obligor for dissolution or
liquidation, the voluntary or involuntary termination or dissolution of any
Obligor or the merger or consolidation of any Obligor with or into another
entity; (f) the insolvency of, the business failure of, the appointment of a
custodian, trustee, liquidator or receiver for or for any of the property of,
the assignment for the benefit of creditors by, or the filing of a petition
under bankruptcy, insolvency or debtor's relief law or the filing of a petition
for any adjustment of indebtedness, composition or extension by or against any
Obligor; (g) that any representation or warranty made to Bank by any Obligor in
any Loan Documents or otherwise was, when it was made, untrue or materially
misleading; (h) the failure of any Obligor to timely deliver such financial
statements, including tax returns, other statements of condition or other
information, as Bank shall request from time to time not remedied within five
(5) business days; (i) the entry of a judgment against any Obligor which Bank
deems to be of a material nature, in Bank's sole discretion not paid or
dismissed within thirty (30) days; (j) the seizure or forfeiture of, or the
issuance of any writ of possession, garnishment or attachment, or any turnover
order for any property of any Obligor; (k) the determination by Bank that it is
insecure for any reason; (l) the determination by Bank that a material adverse
change has occurred in the financial condition of any Obligor; or (m) the
failure of Borrower's business to comply with any material law or regulation
controlling its operation.

11. Remedies upon Default. Whenever there is a default under this Note (a) the
entire balance outstanding hereunder and all other obligations of any Obligor to
Bank (however acquired or evidenced) shall, at the option of Bank, become
immediately due and payable and any obligation of Bank to permit further
borrowing under this Note shall immediately cease and terminate, and/or (b) to
the extent permitted by law, the Rate of interest on the unpaid principal shall
be increased at Bank's discretion up to the Prime Rate plus 5% per annum (the
"Default Rate"). The provisions herein for a Default Rate shall not be deemed to
extend the time for any payment hereunder or to constitute a "grace period"
giving Obligors a right to cure any default. At Bank's option, any accrued and
unpaid interest, fees or charges may, for purposes of computing and accruing
interest on a daily basis after the due date of the Note or any installment
thereof, be deemed to be a part of the principal balance, and interest shall
accrue on a daily compounded basis after such date at the Default Rate provided
in this Note until the entire outstanding balance of principal and interest is
paid in full. Bank is hereby authorized at any time to set off and charge
against any deposit accounts of any Obligor, as well as any money, instruments,
securities, documents, chattel paper, credits, claims, demands, income and any
other property, rights and interests of any Obligor which at any time shall come
into the possession or custody or under the control of Bank or any of its
agents, affiliates or correspondents, without notice or demand, any and all
obligations due hereunder. Additionally, Bank shall have all rights and remedies
available under each of the Loan Documents, as well as all rights and remedies
available at law or in equity.

12. Non-waiver. The failure at any time of Bank to exercise any of its options
or any other rights hereunder shall not constitute a waiver thereof, nor shall
it be a bar to the exercise of any of its options or rights at a later date. All
rights and remedies of Bank shall be cumulative and may be pursued singly,
successively or together, at the option of Bank. The acceptance by Bank of any
partial payment shall not constitute a waiver of any default or of any of Bank's
rights under this Note. No waiver of any of its rights hereunder, and no
modification or amendment of this Note, shall be deemed to be made by Bank
unless the same shall be in writing, duly signed on behalf of Bank; each such
waiver shall apply only with respect to the specific instance involved, and
shall in no way impair the rights of Bank or the obligations of Obligor to Bank
in any other respect at any other time.

13. Applicable Law, Venue and Jurisdiction. This Note and the rights and
obligations of Borrower and Bank shall be governed by and interpreted in
accordance with the law of the State of Maryland. In any litigation in
connection with or to enforce this Note or any endorsement or guaranty of this
Note or any Loan Documents, Obligors, and each of them, irrevocably consent to
and confer personal jurisdiction on the courts of the State of Maryland or the
United States located within the State of Maryland and expressly waive any
objections as to venue in any such courts. Nothing contained herein shall,
however, prevent Bank from bringing any action or exercising any rights within
any other state or jurisdiction or from obtaining personal jurisdiction by any
other means available under applicable law.

14. Partial Invalidity. The unenforceability or invalidity of any provision of
this Note shall not affect the enforceability or validity of any other provision
herein and the invalidity or unenforceability of any provision of this Note or
of the Loan Documents to any person or circumstance shall not affect the
enforceability or validity of such provision as it may apply to other persons or
circumstances.

15. Waiver of Jury Trial. Obligors waive trial by jury in any action or
proceeding to which Obligors and Bank may be parties, arising out of, in
connection with or in any way pertaining to, this Note or the Loan Documents. It
is agreed and understood that this waiver constitutes a waiver of trial by jury
of all claims against all parties to such action or proceedings, including
claims against parties who are not parties to this Note. This waiver is
knowingly, willingly and voluntarily made by Obligors.

                                        2
                                                              Approved: 09-21-95
                                                               Revised: 08-30-99

<PAGE>

16. Binding Effect. This Note shall be binding upon and inure to the benefit of
Borrower, Obligors and Bank and their respective successors, assigns, heirs and
personal representatives, provided, however, that no obligations of Borrower or
Obligors hereunder can be assigned without prior written consent of Bank.

17. Controlling Document. To the extent that this Note conflicts with or is in
any way incompatible with any other Loan Document concerning this obligation,
the Note shall control over any other document, and if the Note does not address
an issue, then each other document shall control to the extent that it deals
most specifically with an issue.

18. ARBITRATION. ANY CONTROVERSY OR CLAIM BETWEEN OR AMONG THE PARTIES HERETO
INCLUDING BUT NOT LIMITED TO THOSE ARISING OUT OF OR RELATING TO THIS
INSTRUMENT, AGREEMENT OR DOCUMENT OR ANY RELATED INSTRUMENTS, AGREEMENTS OR
DOCUMENTS, INCLUDING ANY CLAIM BASED ON OR ARISING FROM AN ALLEGED TORT, SHALL
BE DETERMINED BY BINDING ARBITRATION IN ACCORDANCE WITH THE FEDERAL ARBITRATION
ACT (OR IF NOT APPLICABLE, THE APPLICABLE STATE LAW,) THE RULES OF PRACTICE AND
PROCEDURE FOR THE ARBITRATION OF COMMERCIAL DISPUTES OF J.A.M.S./ENDISPUTE OR
ANY SUCCESOR THEREOF (J.A.M.S.), AND THE "SPECIAL RULES" SET FORTH BELOW. IN THE
EVENT OF ANY INCONSISTENCY, THE SPECIAL RULES SHALL CONTROL. JUDGMENT UPON ANY
ARBITRATION AWARD MAY BE ENTERED IN ANY COURT HAVING JURISDICTION. ANY PARTY TO
THIS INSTRUMENT, AGREEMENT OR DOCUMENT MAY BRING AN ACTION, INCLUDING A SUMMARY
OR EXPEDITED PROCEEDING, TO COMPEL ARBITRATION OF ANY CONTROVERSY OR CLAIM TO
WHICH THIS AGREEMENT APPLIES IN ANY COURT HAVING JURISDICTION OVER SUCH ACTION.

A. SPECIAL RULES. THE ARBITRATION SHALL BE CONDUCTED IN THE COUNTY OF ANY
BORROWER'S DOMICILE AT THE TIME OF THE EXECUTION OF THIS INSTRUMENT, AGREEMENT
OR DOCUMENT AND ADMINISTERED BY J.A.M.S. WHO WILL APPOINT AN ARBITRATIOR; IF
J.A.M.S. IS UNABLE OR LEGALLY PRECLUDED FROM ADMINISTERING THE ARBITRATION, THEN
THE AMERICAN ARBITRATION ASSOCIATION WILL SERVE. ALL ARBITRATION HEARINGS WILL
BE COMMENCED WITHIN 90 DAYS OF THE DEMAND FOR ARBITRATION; FURTHER, THE
ARBITRATOR SHALL ONLY, UPON A SHOWING OF CAUSE, BE PERMITTED TO EXTEND THE
COMMENCEMENT OF SUCH HEARING FOR UP TO AN ADDITIONAL 60 DAYS.

B. RESERVATION OF RIGHTS. NOTHING IN THIS ARBITRATION PROVISION SHALL BE DEEMED
TO (I) LIMIT THE APPLICABILITY OF ANY OTHERWISE APPLICABLE STATUTES OF
LIMITATION OR REPOSE AND ANY WAIVERS CONTAINED IN THIS INSTRUMENT, AGREEMENT OR
DOCUMENT; OR (II) BE A WAIVER BY BANK OF THE PROTECTION AFFORDED TO IT BY 12
U.S.C. SEC. 91 OR ANY SUBSTANTIALLY EQUIVALENT STATE LAW; OR (III) LIMIT THE
RIGHT OF BANK HERETO (A) TO EXERCISE SELF HELP REMEDIES SUCH AS (BUT NOT LIMITED
TO) SETOFF, OR (B) TO FORECLOSE AGAINST ANY REAL OR PERSONAL PROPERTY
COLLATERAL, OR (C) TO OBTAIN FROM A COURT PROVISIONAL OR ANCILLARY REMEDIES SUCH
AS ( BUT NOT LIMITED TO) INJUNCTIVE RELIEF, WRIT OF POSSESSION OR THE
APPOINTMENT OF A RECEIVER. BANK MAY EXERCISE SUCH SELF HELP RIGHTS, FORECLOSE
UPON SUCH PROPERTY, OR OBTAIN SUCH PROVISIONAL OR ANCILLARY REMEDIES BEFORE,
DURING OR AFTER THE PENDENCY OF ANY ARBITRATION PROCEEDING BROUGHT PURSUANT TO
THIS INSTRUMENT, AGREEMENT OR DOCUMENT. NEITHER THIS EXERCISE OF SELF HELP
REMEDIES NOR THE INSTITUTION OR MAINTENANCE OF AN ACTION FOR FORECLOSURE OR
PROVISIONAL OR ANCILLARY REMEDIES SHALL CONSTITUTE A WAIVER OF THE RIGHT OF ANY
PARTY, INCLUDING THE CLAIMANT IN ANY SUCH ACTION, TO ARBITRATE THE MERITS OF THE
CONTROVERSY OR CLAIM OCCASIONING RESORT TO SUCH REMEDIES.

Borrower represents to Bank that the proceeds of this loan are to be used
primarily for business, commercial or agricultural purposes. Borrower
acknowledges having read and understood, and agrees to be bound by, all terms
and conditions of this Note, and hereby executes this Note intending to create
an instrument executed under seal.

NOTICE OF FINAL AGREEMENT. THIS WRITTEN PROMISSORY NOTE REPRESENTS THE FINAL
AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS.

Corporate or Partnership Borrower

OPNET Technologies, Inc.
------------------------

By:___________________________  (Seal)

Name:_________________________

Title:________________________


______________________________
Attest (If Applicable)


[Corporate Seal]

                                        3
                                                              Approved: 09-21-95
                                                               Revised: 08-30-99