He was 76.
Meszaros died at Providence Little Company of Mary Medical Center in Torrance, California, said manager Dennis Varga.
A few days ago, the actor had been found unresponsive in the home in nearby Hawthorne that he shared with Varga, said the Hollywood Reporter.
Meszaros donned the furry, dog-like costume with the big snoot on ALF, which aired for four seasons (1986-90), on a handful of the show's 102 episodes.
Most of the time, the extraterrestrial character ALF (an acronym for Alien Life Form) when seen on the series was a puppet piloted by the show's co-creator, Paul Fusco.
Michael Jackson saw him perform and they became close friends and appeared together in a soft drink commercial.