The suspect walked up to a teller at the Citibank at 1888 Ralston Ave. and presented a note demanding money at about 9:25 a.m., according to the Belmont Police Department. He was armed with a handgun, police said.
The teller handed over an undisclosed amount of cash, and the robber fled on foot. No one was injured in the robbery.
The suspect was described as a middle-aged man wearing a dark jacket and hat, police said.
FBI agents are assisting Belmont police with the investigation.
Anyone with information about the case is asked to contact Belmont police at (650) 595-7400.