The 28-year-old Twilight alum was spotted in the crowd as she performed on Saturday, day 2 of the double weekend annual event in Indio, California.
The two later reunited offstage at an after party, the Moschino Late Night event with Jeremy Scott, sponsored by DeLeón Tequila.
Pattinson and the singer began dating last fall and source told E! News earlier this month that they are engaged. FKA Twigs, whose real name is Tahliah Barnett, was not spotted wearing an engagement ring at the after party, an eyewitness told E! News.
The two shared a few kisses while chatting with friends, E! News has learned.
"They spent most of the time talking to other people but when they were together they were really cute," the witness said about FKA Twigs and Pattinson. "You can tell they're really happy together."