The National Highway Traffic Safety Administration says the problem could affect 830,000 vehicles.
The safety agency says in documents on its website that the fires appear to start in the power window switch on the door. Six fires have been reported to the agency. No one has been hurt.
The Camry is the top-selling car in the U.S., and the RAV-4 also is a consistent top seller for Toyota. The probe also includes the Solara, which is a coupe version of the Camry.
The investigation was opened Monday. It could lead to a recall, but there isn't one yet.