The incident began at around 10 a.m. at the corner of Huntington Drive and Myrtle Avenue.
Police say a man shoved a note under the door of the closed bank claiming that he had a bomb and he demanded money.
Officials say that the note was similar to one used in an earlier bank robbery in Pasadena.
The bank refused to open the door, but the man barricaded himself inside the foyer.
The police responded and they ended up evacuating about 500 people from the bank building as well as several businesses. They also locked down a parameter until more police arrived at the scene to deal with the man who was still in the bank's foyer.
"Officers eventually did make contact with that individual and were able to talk him out and surrendered to police authorities," said Capt. Alan Sanvictores of Monrovia police. "That particular individual is in custody at the Monrovia Police Department for attempted bank robbery at the moment and other than that, the investigation is still continuing."
The standoff went on for approximately four hours. Police strip searched him and then arrested him. The Foothill Special Enforcement SWAT team, a regional tactical unit comprised of Monrovia, Irwindale, San Marino, Laverne and Glendora police departments, was brought in. The FBI and the LAPD were also brought in.
By late afternoon, all of the 500 evacuees have been allowed into the building.