The "guest list was getting out of control so she decided to cancel," a source said.
However, Winfrey and about 50 friends marked the occasion in a low-key fashion last Friday by taking a spinning class at SoulCycle in West Hollywood.
"I just had the best birthday experience ever at SoulCycle," Winfrey said in a video she posted on her Instagram account after the class.
E! News said all the guests in the class wore blue shirts with "Happy Birthday Oprah" written in big green letters, while instructor Angela Davis included many of Winfrey's favorite songs during the 45-minute workout.
Winfrey will turn 60 Wednesday.