The Healdsburg Fire Department located the vehicle in the 8700 block of Mill Creek Road at about 4:15 a.m., Lt. Steve Brown said.
Firefighters extinguished the blaze and contacted the California Highway Patrol believing there had been a car accident, Brown said.
The CHP called the sheriff's office after a body was discovered inside the car, Brown said.
Sheriff's Capt. Matt McCaffrey said this afternoon it doesn't appear there was a crash.
"We're not sure if it was a suicide, homicide or accidental death. There was no obvious cause of death. Nothing points in one direction or another," McCaffrey said.