The West Aussie drag racing venue had been hosting the Outlaw Nitro Challenge when a shooting incident took place at 8:36pm.
According to WA Police two victims were treated at the scene before being taken to hospital.
Witnesses are being urged to contact Crime Stoppers on 1800 333 000.
Local media is reporting that the gang crime squad is investigating the matter.
Perth Motorplex has been the scene of motorcycle gang violence in the past, three members of the Finks hospitalised back in 2010 after an altercation with rival gang the Coffin Cheaters.