The suspect entered a First Convenience Bank branch at around 11:30 a.m. wearing a baseball cap, dreadlock wig, sunglasses and white gauze covering his face and right hand.
He approached the teller and verbally threatened her while demanding cash, the FBI said in a news release.
He fled with an undisclosed amount of cash and got into a black Mitsubishi Montero SUV being driven by someone else.
"It's a little early for Halloween," FBI spokesman Connor Hagen told Fox News. "This guy did go into a regular business ... he terrorized the tellers, and these were people going about their everyday business."
No one was injured during the robbery, the FBI said.
The robber was described as a black male in his early 20s, 5 feet 11 inches tall with a medium build. A $5,000 cash reward is being offered for information leading to his identification and arrest.
"We're hoping to wrap this case up quickly," Hagen said.