The car-to-car shooting was reported by the victim shortly before midnight on the eastbound side of the freeway, near Francisquito Avenue, a CHP spokesperson said.
The wounded man followed the suspect's vehicle while talking on the phone with the Highway Patrol, and CHP officers conducted a traffic stop in Pomona.
The unidentified suspect pulled over and was taken into custody without incident. A firearm -- either a BB gun or an airsoft gun -- was recovered, authorities said.
Two other people in the suspect's vehicle were detained but not arrested.
The shooting victim was evaluated at the scene but not transported to a hospital, according to the Highway Patrol.
The suspected gunman suffered an unknown injury and was taken to a hospital for treatment, the CHP spokesperson said.
The motive for the shooting was under investigation.