The incident happened on the 1700 block of East Katella Avenue shortly after 1 p.m. Thursday.
Police say the robber demanded cash. He told the teller that he had a gun but didn't show one.
The suspect was caught on surveillance camera. He was described as a Hispanic man about 30-40 years old, between 5 feet 6 inches and 5 feet 10 inches tall with black hair. He was wearing a dark shirt and dark sunglasses.
No one was hurt during the heist.
If you have information on the suspect, you're urged to contact Orange County Crime Stoppers at (855) TIP-OCCS or (855) 847-6227.