It happened at 11:46 a.m. at 1701 Harrison Ave., near Weston Parkway.
Authorities say a man entered the bank, implied he had a weapon, and then fled on foot with a tray of money.
No injuries were reported during the incident.
Police described the suspect as a white man wearing a brown fur trapper hat and sunglasses and a black cloth around his face. He is also described as being between 5-10 and 6-1 and wearing a black jacket.
Images from Chopper11 HD showed police officers and a police K-9 searching the area for the man. The bank was closed for several hours following the robbery.
If you have any information on the bank robber, please call Cary Police at (919) 469-4013.