The Keystone B-3A was a bomber aircraft developed for the United States Army Air Corps by Keystone Aircraft in the late 1920s.

The B-3 was originally ordered as the LB-10A (a single-tail modification of the Keystone LB-6), but the Army dropped the LB- 'light bomber' designation in 1930.

Although the performance of the B-3A was hardly better than that of the bombers flown at the end of World War I, it had come a long way in terms of flight safety.

The B-3A was a member of the last family of biplanes operated by the US Army; it remained in service until 1940.

A few years after it was first produced, the introduction of all-metal monoplanes rendered it almost completely obsolete.