The robberies, which were partially captured on surveillance cameras, happened last week.
On Thursday, the suspect demanded cash from a teller at a U.S. Bank inside an Albertsons in Costa Mesa, police said.
The next day, the same suspect allegedly robbed another U.S. Bank inside a Ralphs in Aliso Viejo.
Both robberies happened around 7 p.m. No one was injured.
If you recognize the suspect or have any relevant information about the robberies, you're urged to contact the FBI at (310) 477-6565.