National Park Service officials say the incident occurred about 10:30 AM Thursday at the fueling station at Antelope Point.
A witness says the victim had fueling his 30-foot cabin motor cruiser and tried to start the engine several times before the boat exploded in flames.
The victim crawled out of the boat and onto the dock, where he was attended to by people in the area and by public safety responders.
The name of the 63-year-old man isn't immediately available.
Authorities say he's been flown to the University of Utah Burn Unit in Salt Lake City.
Coconino County Sheriff's deputies in northern Arizona are investigating the incident.