In the absence of any law to the contrary, it should well be. A new bill is working its way through the Nevada state legislature that would remove any doubt in that state. A.B. 511 directs the Nevada Department of Transportation to authorize autonomous vehicle testing in certain geographic areas of Nevada. Should vehicles meet Nevada DOT standards, they would be permitted to "operate on a highway."
The bill defines not only autonomous vehicle, but artificial intelligence as well. AI is "the use of computers and related equipment to enable a machine to duplicate or mimic the behavior of human beings." An autonomous vehicle uses "artificial intelligence, sensors, and [GPS] coordinates to drive itself." (Source)