Mr Mercanti was home when the fire started in his garage late on Wednesday night.
A department spokeswoman said four fire crews were called to the blaze on Shepherds Bush Drive at 11.45pm. It took about two hours to contain the fire, which caused about $175,000 damage.
Mr Mercanti was a regular feature on TV with his cover act Slim Jim and the Phatts in the ’90s.
He remains a recognizable face in Perth entertainment.