Japan's Ministry of Economy, Trade, and Industry is examining three reports of overheating iPod Nanos sparking fires, Reuters reported.
The government agency said Apple had reported two other cases in which people had suffered minor burns.
The trade ministry said iPod Nanos with known overheating incidents were sold in Japan between September 2005 and September 2006.
Faulty batteries may be the cause of the incidents, the agency said.
Batteries have been traced to a host of issues with laptops and other mobile devices. Apple was one of several companies that had to recall notebooks in 2006 after problems led to overheating and fires.
Apple officials could not immediately be reached for comment.