The robbery occurred at the Westamerica Bank at 3515 Mt. Diablo Blvd. around 10 a.m., according to police.
Police said multiple schools in the surrounding area were placed on lockdown as a precaution. Officers were searching the area with the help of a police K-9.
The robbery suspect was described as a white man in his 20s wearing a baseball cap, sunglasses and a navy-blue button-down, long-sleeve shirt, according to police.
Anyone who noticed anything suspicious or out of the ordinary in the area was encouraged to call 911.
Police said shortly before 11 a.m. that the lockdowns had been lifted. They have not yet provided more details about the incident.