Billionaire entrepreneur Elon Musk is concerned about artificial intelligence. In fact, the inventor of the private spaceflight company SpaceX and the car company Tesla says that AI is humanity's "biggest existential threat."

"I think we should be very careful about artificial intelligence," Musk said in response to an audience question during a Q&A on Friday (Oct. 24). "If I were to guess at what our biggest existential threat is, it's probably that, so we need to be very careful with artificial intelligence. I'm increasingly inclined to think that there should be some regulatory oversight, maybe at the national and international level just to make sure that we don't do something very foolish."

Musk explained his views on AI, referring to intelligent machines, when he took questions from the audience at the Massachusetts Institute of Technology's AeroAstro 100 conference celebrating the 100th anniversary of the university's aeronautics and astronautics department. [The History of Artificial Intelligence (Infographic)]

"With artificial intelligence, we are summoning the demon," Musk added. "You know all those stories where there's the guy with the pentagram and the holy water and … he's sure he can control the demon. It doesn't work out."

The SpaceX founder went on to say that HAL 9000 — the murderous artificially intelligent computer from "2001: A Space Odyssey" — would be "like a puppy dog" compared to the AI he's imagining.

Musk had to ask the next person asking a question to repeat herself, because he was so caught up in thinking about artificial intelligence.

This isn't the first time Musk has made his views on AI known. In August, Musk wrote about his feelings on artificial intelligence on Twitter, according to Mashable.

"We need to be super careful with AI. Potentially more dangerous than nukes," Musk tweeted on Aug. 2, 2014, after recommending a book about AI called "Superintelligence" (Oxford University Press, 2014) written by Nick Bostrom.

Musk is also putting his money where his worries are. Last year, actor Ashton Kutcher, Facebook inventor Mark Zuckerberg and Musk invested $40 million in the company Vicarious FPC, which is planning to build an artificial brain that can think like a person.

While it may seem odd that Musk is investing in AI, in June, he told CNBC that he'd like to "keep an eye on what's going on with artificial intelligence. I think there's potentially a dangerous outcome there."

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