Police said a man entered the bank at 1:52 p.m. and told a teller he had a weapon. He took cash and fled.
Witnesses told police the suspect was a black man, about 6-foot-1 and in his late 20s or early 30s.
Police are trying to determine whether the robbery is connected to another one in Reston two weeks ago or two that occurred in the McLean District in the last week.
Reston Now will add additional details as we get them.