The robbery was reported at 1:37 p.m. at the Washington Mutual bank branch at 1390 S. Main St., police said.
Two men reportedly entered the bank and demanded money. The tellers complied and the men fled the bank with the case.
No weapons were seen and nobody was hurt, Barrett said.
One of the robbers was seen riding a bicycle south away from the bank, Barrett said.
Police responded within minutes of the robbery and began searching the area with help from police dogs and a California Highway Patrol helicopter.
Officers later found the bike used as a getaway vehicle, but didn't find either of the suspects, Barrett said.
Las Lomas High School, which is just down the street at 1460 S. Main St., was placed on lockdown as a precaution, Barrett said.
The lockdown was lifted and students were released at around 3:45 p.m., Barrett said.
The first suspect was described as a black man between 30 and 40 years old with a medium build, black hair and brown eyes. He had a graying beard and was last seen wearing a black shirt with vertical white stripes, Barrett said.
The second suspect was described as a black man about 25 years old, about 5 feet 10 inches tall and weighing between 170 and 180 pounds. He had black hair and a black goatee and was last seen wearing a dark shirt and blue jeans.