The incident, which began shortly after noon, required trains in both directions to be shut down in the Long Beach area, said Lt. Mark Lucio of the Los Angeles County Sheriff's Department's Transit Bureau.
"He claimed he had a bomb and he was going to blow up the train," Lucio said. "We had K-9 dogs sweep the area and no bombs were found and no explosives were found."
Lucio said the suspect, whose name was withheld Friday, was arrested on a charge of making criminal threats on a train and was booked at the Century City Sheriff's Station jail.
He is expected to be arraigned next week.
Blue Line Service was fully restored shortly before 1 p.m., MTA officials said.