Page 1

( Mark One ) ☑ UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 ☐ For the fiscal year ended December 31 , 2020 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 FOR THE TRANSITION PERIOD FROM ΤΟ Commission File Number 001-38817 MainStreet Bancshares , Inc. ( Exact name of Registrant as specified in its Charter ) Virginia ( State or other jurisdiction of incorporation or organization ) 10089 Fairfax Boulevard Fairfax , VA ( Address of principal executive offices ) Securities registered pursuant to Section 12 ( b ) of the Act : Registrant's telephone number , including area code : ( 703 ) 481-4567 Title of each class Common Stock Depositary Shares ( each representing a 1 / 40th interest in a share of 7.50 % Series A Fixed - Rate Non - Cumulative Perpetual Preferred Stock ) Trading Symbol ( s ) MNSB MNSBP 81-2871064 ( I.R.S. Employer Identification No. ) 22030 ( Zip Code ) Name of each exchange on which registered The Nasdaq Stock Market LLC The Nasdaq Stock Market LLC Securities registered pursuant to Section 12 ( g ) of the Act : None Indicate by check mark if the Registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . YES NO Indicate by check mark if the Registrant is not required to file reports pursuant to Section 13 or 15 ( d ) of the Act . YES NO Indicate by check mark whether the Registrant : ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the Registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . YES NO □ Indicate by check mark whether the Registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( $ 232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the Registrant was required to submit such files ) . YES NO □ Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , " " smaller reporting company , " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . Large accelerated filer Non - accelerated filer Emerging growth company ☐ ☑ Accelerated filer Smaller reporting company ☐ If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . ☑ Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . ☐ Indicate by check mark whether the Registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . YES NO As of June 30 , 2020 , the last business day of the Registrant's most recently completed second fiscal quarter , the aggregate market value of the shares of common equity held by non - affiliates of the Registrant , based on the closing price of the shares of common stock on The NASDAQ Stock Market , was $ 104,561,424 . The number of shares of Registrant's Common Stock outstanding as of March 18 , 2021 was 7,544,532 . DOCUMENTS INCORPORATED BY REFERENCE : The information required by Part III of this Annual Report on Form 10 - K will be found in the Company's definitive proxy statement for its 2021 Annual Meeting of Shareholders , to be filed pursuant to Regulation 14A under the Securities Exchange Act of 1934 , and such information is incorporated herein by this reference .