Images of the self-driving Tesla, without anybody in the front of the vehicle, were reported to CHP at the weekend.
CHP confirmed on Saturday that the incident was the focus of an investigation, in a statement on Facebook, and said the images were “third party information”.
“CHP has been made aware of an incident involving a man riding in the backseat of a Tesla travelling on Bay Area roadways, with no other person being seated in the driver seat,” the CHP wrote.
“Safety for all who share our roadways is the primary concern of the CHP,” it added – calling for further information.
Although Teslas are fitted with technology for future self-driving capabilities, according to the California firm, the ‘autopilot’ feature is not currently in widespread use.
In fact, Tesla founder Elon Musk is among a few drivers with access to the firm’s "full self-driving" (FSD) feature – as are a small number of Tesla employees, and customers.
As reported by Reuters, Mr Musk told California regulators in January that the firm was “highly confident the car will be able to drive itself with reliability in excess of human this year”.
Saturday’s incident follows a fatal Tesla crash in Fontana, California, last Wednesday. The incident is also the focus of CHP investigation.
In another incident, in Texas, investigators recently ruled that the autopilot feature was not in full use during a fatal accident. Federal investigators are investigating a further 24 incidents of Tesla crashes allegedly featuring autopilot.
The Independent has approached Tesla for comment.