Authorities said the victim was stabbed in the leg and taken to a hospital in stable condition. The injury was described as not life-threatening.
Deputies responded around 11:22 a.m. to the area of Long Beach Boulevard and Norton Avenue after a report of a disturbance on a Metro bus, according to the Los Angeles County Sheriff's Department.
A person of interest was taken into custody about a block and a half away from the scene.
AIR7 HD was over the intersection where several sheriff's deputies were standing near the bus.
It's unclear what led up to the stabbing. A man who was nearby said he heard two people yelling at each other at the bus stop.
Metro said in a statement it shares the concerns of its employees and customers about "the increased severity of crime we are seeing in our cities and on the Metro system."
"Metro hopes for a swift and full recovery to the victim and commends the Los Angeles Sheriff's Department for their prompt action in apprehending the suspect," Metro said.
Anyone with information about the stabbing was asked to contact the Sheriff Department's Transit Services Bureau at 323-563-5000.