The book referred to in Musk's tweet is Superintelligence: Paths, Strategies, Dangers by Nick Bostrom.
It's not the first time Musk's aired such concerns. In June, he told CNBC that artificial intelligence is "potentially dangerous."
"There's some scary outcomes and we should try to make sure the outcomes are good, not bad," he said on CNBC's "Closing Bell."
Musk recently invested in artificial intelligence company Vicarious, though he said the move is mostly to "keep an eye on what's going on with artificial intelligence."
Even though his concerns were echoed by renowned physicist Stephen Hawking, Musk's musings at the time brought some ridicule.
Venture capitalist, musician, and Elevation Partners co-founder Roger McNamee largely dismissed the AI threat.
"If you want something to worry about, just read the newspaper," he told CNBC's "Squawk Alley." "There's a good chance we will have polluted the Earth beyond repair before they get any of this AI stuff to work."