The stabbing happened just before 5:20 p.m. after an argument between two men, according to the Los Angeles Police Department.
Police said the suspect took out a knife and stabbed the 23-year-old victim.
The victim was taken to a hospital, where he was pronounced dead.
The suspect fled the scene and remains on the loose, police said.
"It is distressing that a senseless act of violence occurred within our Metro system," Metro said in a statement. "Safety is, and always has been Metro's utmost priority and we are deeply committed to providing a secure environment for our customers. Metro is working with the Los Angeles Police Department to investigate this incident."
A police investigation caused trains to bypass the station, Metro's Patrick Chandler told City News Service.
City News Service contributed to this report.