UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of July 2014

Commission File Number: 000-53445

KB Financial Group Inc.

(Translation of registrant’s name into English)

84, Namdaemoon-ro, Jung-gu, Seoul 100-703, Korea

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F   x            Form 40-F  ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):  ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):  ¨

Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

Yes  ¨            No   x

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): 82-N/A.

2014 First Half Preliminary Operating Results

On July 25, 2014, KB Financial Group Inc. (“KB Financial Group”) held an earnings conference and released its preliminary operating results for the first half of fiscal year 2014. The following tables reflect the key figures released during the conference. The presentation materials for the conference, which contain further details, are available at KB Financial Group’s website (http://www.kbfg.com).

The preliminary figures presented herein are based on the International Financial Reporting Standards as adopted by the Republic of Korea (“K-IFRS”) and are currently being reviewed by our independent auditors and are subject to change.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.