While casinos recognize the value poker players offer, many poker players feel they aren't fully appreciated by the casinos. Poker rooms are sometimes placed in undesirable locations within the casino and comps are meager compared to those doled out to players of other casino games.
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.