Deputies detained three juveniles on the Metro Blue Line on Tuesday evening after receiving a report that they were armed with guns, law enforcement authorities said.
The three were detained at the Willow Station while deputies searched the train, according to the Los Angeles County Sheriff's Department.
The search temporarily delayed Blue Line service, Metro said.
The deputies were assisted by Long Beach police as they searched the train with their guns drawn.
No weapons were found and the three teens were released, said Lt. Barry Shapiro of the Sheriff's Department's transit unit, which patrols the train lines.
The incident was cleared around 7 p.m. and normal train service was resumed.