When a group of young Justin Bieber fans agreed to participate in a focus group to test out the pop star's new song in the video game "Just Dance 4," the last thing they were expecting was that the man himself would be watching them.
After the girls started playing the game, Bieber quietly comes into the room and starts dancing until the girls notice he's there. Watch the video above to see their priceless reactions -- from screams to sobs to swearing -- for yourself.
Die-hard fans know that the Biebs is full of surprises. This week, Bieber surprised another fan at one of his concerts -- this time it was Megan Ham, an 11-year-old with a neurological disorder who always dreamed of meeting the star. Although the girl can't walk or talk, when she hears Justin Bieber's music, she starts to kick and smile. Her dream came true when she had a private meeting with Bieber before his concert at the Rose Garden in Arizona.
And last week, the "Boyfriend" singer surprised fans in LA by showing up on a segway for an unexpected meet-and-greet , high-fiving the young finalists from the Disney Channel's Make Your Mark: Shake It Up Dance Off.
What did you think of the fans' reactions? What would you do if you got a surprise visit from Justin Bieber? Tell us in the comments below or tweet @HuffPostTeen!