The fire started about 4.30pm before two units from the Joondalup Fire Station extinguished it in half an hour.
Police want to talk with two teenagers seen leaving the bushland near West Coast Institute. They are described as dark skinned, 15 to 16 years of age with skinny builds.
One of the boys wore a dark green jumper, while the other wore a dark blue one and had dark medium straight hair.
They were last seen heading towards Joondalup train station. Anyone with any information can call the Joondalup Police on 9400 0888.