Yes, online poker is legal in the United States, albeit only in certain states. As of early 2024, only six states have legalized online poker  Nevada, Delaware, New Jersey, Pennsylvania, West Virginia, and Michigan.
On April 15, 2011, the U.S. Attorney's Office for the Southern District of New York seized and shut down Pokerstars and several of its competitors' sites, alleging that the sites were violating federal bank fraud and money laundering laws.