The robbery attempt was reported at 3:54 p.m. at the Bank of America at 3812 San Fernando Road.
Police say one suspect went inside the bank and told the teller he had a device and demanded money. The teller handed over an undisclosed amount of cash.
While that was happening, police were already detaining a second suspect outside the location. When the initial suspect left the bank, he too was taken into custody.
In the meantime, the suspect left behind a bag at the bank. Police are waiting for the Los Angeles County Sheriff's Department bomb squad to investigate the bag.
No one was injured. Streets in the area were closed as police investigated.