Although the Oscar winners have stayed mum about the nature of their relationship, they were quite comfortable showing their affection for each other at Penn's Help Haiti Home gala Saturday night at the Montage hotel in Beverly Hills, Calif.
Theron and Penn didn't pose on the red carpet together, but things heated up inside the event, with the Prometheus star putting her arm around Penn when he sat down beside her at a table in the middle of the ballroom. He then gave her a few kisses on her neck, and they shared a sweet kiss on the lips.
Tonight's charity gala, which benefits the J/P HRO, marked the pair's first official public appearance.
The duo was last spotted out enjoying a date night at ArcLight Cinemas in Hollywood Sunday, Jan. 5, and seemed "really casual and comfortable" when they left the movie, an eyewitness told E! News.
The 38-year-old actress and her 53-year-old beau have been spending a great deal of time together as of late, also taking time to relax in Hawaii during a holiday getaway last month.
When they returned to Los Angeles after the New Year, Theron and Penn continued to hang out, spending time at Penn's Malibu, Calif. home.
"They are spending night after night together and moving very fast," a source told E! News exclusively. "It seems like it's getting serious and that they can't get enough of each other."