There are currently 5 states that offer legal online poker for real money in the United States  New Jersey, Nevada, Pennsylvania, Michigan, and Delaware.

California Penal Code 330 PC prohibits gambling, also called gaming, by the use of a banking or percentage game.  That said, it is still lawful in California to play social poker games and other games of chance, skill, and strategy involving individual bets.

Play for Fun: You can play poker with friends or family just for the fun of it. Use chips or tokens instead of real money to keep track of bets and pots. This is a great way to practice your poker skills and enjoy the social aspect of the game without any financial risk.

Fortunately, in Penal Code Sec. 337j(e)(2)(D) we're told that games played with cards in a private home where no one profits from the running of the game are 100% fine. So yes, since online poker is played at home with the only gains being your winnings, it's perfectly legal.