The Justice Department is looking into the legality of the claim that the cars can drive on their own.
Three people with knowledge of the probe told the news outlet that the investigation was launched after a series of accidents where the cars' autopilot systems were enabled.
It's not clear what the status of the investigation is and whether prosecutors intend to bring any charges.
Forbes did not get a response from Musk or the Justice Department.
The "Full Self-Driving Capability" of some of its vehicles, as well as the "Autopilot" system, requires active driver supervision and do not make the vehicle autonomously.
Despite a broad downturn in tech stocks, the news didn't have a negative impact onTesla stock, which was flat in after-hours trading.
In the past, Musk promised to have 1 million robotaxis by the end of the year, but he's toned it down recently. The billionaire said last week during a conference call that its cars are not ready to have no one driving them. Musk has pushed back against reports of accidents involving self- driving vehicles. He responded to a claim that there had been no accidents or injuries since the Full-Self Driving feature was launched. The agency launched an investigation into the company last year to see if a recall is needed. The investigation is still going on.
The takeover bid by Musk is expected to be finalized on Friday.
We think Musk is the richest person in the world because of his share of the company.
The U.S. is investigating self-driving claims byTesla.
The deal appears to be close.
The stock dropped after missing revenue expectations.