Fairfax County Police said the PNC Bank inside the Giant at North Point Village Center was robbed about 5 p.m. Monday.
The suspect told a teller he had a weapon and then got away with an undisclosed amount of money, police spokesman Lucy Caldwell said. Police did not yet have a description of the suspect Monday evening.
This is the fourth bank robbery in Reston in the last several weeks.
On Dec. 15, the Sun Trust inside the Safeway at Hunters Woods Village Center was robbed.
On Dec. 10, there was a robbery at the Wells Fargo Branch at Reston Town Center.
Police are working with the Federal Bureau of Investigation to see whether the incidents are related, Caldwell said.
The FBI said recently that December is the busiest month for bank robberies.