A Hollywood film insider recently revealed the news to Radar Online.
"Jack has -- without fanfare -- retired," said the source.
"There is a simple reason behind his decision -- it's memory loss. Quite frankly, at 76, Jack has memory issues and can no longer remember the lines being asked of him."
The silver screen has seen less of the Oscar winner in recent years. He hasn't appeared in a film since "How Do You Know" in 2010.
Nicholson has starred in films including "The Shining," "Terms of Endearment," "Batman," "One Flew Over the Cuckoo's Nest" and "As Good as It Gets," among many others.
Nicholson or his camp have yet to make an official announcement.