The fire burning east of Mt Helena has been contained, but nearby residents are asked to stay vigilant.
The blaze was brought under control by Department of Environment and Conservation firefighters, with the help of volunteer crews from the Shire of Mundaring.
It burned through about two hectares 3.5km east of Eastern Hills Senior High School.
Elliott Road remains closed between Matheson Road and Lion Road.
Aircraft have been sent to help fire crews battle the blaze.
The fire has been deemed suspicious.
Anyone with information is urged to call Crime Stoppers on 1800 333 000.