It was found about 11:30 p.m. Sunday when Riverside County firefighters put out the flames inside the car off Van Buren Boulevard and the 215 Freeway.
Crews first responded to the scene after reports of a fire.
Authorities have not said if the person inside is a man or a woman.It's unclear how that victim died.
Officials were calling the incident an active death investigation, the Riverside County Sheriff's Department said on Twitter.
City News Service contributed to this report.