The Warriors confirmed as such on Thursday, while issuing an apology for Stevens' actions.
Toronto's Lowry flew into the seats while chasing after the ball early in the fourth quarter, landing on several courtside spectators.
He was trying to regain his balance when Stevens reached over two seats and shoved the Raptors star.
"Mr. Stevens' behaviour last night did not reflect the high standards that we hope to exemplify as an organisation," the Warriors' statement read.
"We're extremely disappointed in his actions and, along with Mr. Stevens, offer our sincere apology to Kyle Lowry and the Toronto Raptors organisation for this unfortunate misconduct.
"There is no place for such interaction between fans - or anyone - and players at an NBA game."
NBA spokesman Mike Bass issued a similar statement, saying Stevens will not be permitted to attend games as the league reviews the incident.
"A team representative must be held to the highest possible standard and the conduct of Golden State Warriors investor Mark Stevens last night was beyond unacceptable and has no place in our league," the statement read.
Stevens was later escorted out of Oracle Arena, and the Warriors announced he will not attend any of the remaining NBA Finals games.
Lowry was frustrated after the game, calling for the NBA to permanently ban the spectator.
"The fans have a place; we love our fans," Lowry told ESPN. "But fans like that shouldn't be allowed to be in there, because it's not right. I can't do nothing to protect myself.
"But the league does a good job, and hopefully they ban him from all NBA games forever."
National Basketball Players' Association (NBPA) president Michelle Roberts also released a statement on Thursday expressing her concern over the incident.
"We are closely monitoring both the Warriors' and the league's continued investigation into this matter and anxiously await their conclusions and response," Roberts' statement read.
"The NBPA has previously expressed its support of a 'zero-tolerance' policy with respect to verbal and/or physical assaults perpetrated against players. Stevens' status as a member of the ownership group does not alter that view."
Photo Getty Images. Caption: Kyle Lowry