UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) X QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2019 or ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from ___________ to ___________ Commission File Number 001-36613 Middlefield Banc Corp. (Exact Name of Registrant as Specified in its Charter) Incorporation or Org ...

(Mark One) Commission file number 001-36613 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 X ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2018 FORM 10-K or TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from ___________ to ___________ . Middlefield Banc Corp. (Exact Name of Registrant as Specified in its Charter) Ohio 34-1585111 State or ...