The "Terminator" actor went undercover to promote fitness at a Gold's Gym in Venice, California as a general manager. He's currently raising awareness for After-School All-Star, a charity which provides kids with free after-school programs, through a partnership with fundraising site Omaze.
Most people didn't realize they were being giving tips by the famous actor who was going by the name Howard.
You could tell a few people caught on to the actor toward the end of the video. After all, he wasn't wearing much of a disguise - just a wig and mustache.
Schwarzenegger shared the video on Reddit yesterday. It already has more than 1 million views.
For more on the charity and to win a ride in a tank with Schwarzenegger, you can head here.