The robbery was reported at 5:53 p.m. at the Chase bank at 1201 Market St. at the intersection of Eighth Street.
The suspect, later identified as 48-year-old Antioch resident Deann Olivia Lopez, walked into the bank and gave a note to an employee demanding money, police spokesman Officer Albie Esparza said.
The employee gave money to Lopez, who then went and sat in the lobby of the bank, Esparza said.
Officers responded to the report of the robbery and took Lopez into custody, Esparza said. He said she didn't say why she remained at the bank following the heist.
No one was injured during the robbery.
Lopez was booked into county jail on suspicion of robbery and burglary, Esparza said.