The former `O.C.` actress is dating British DJ Ali Love and the couple went public with their romance at London festival Lovebox over the weekend, where onlookers say they couldn`t keep tier hands off each other.
A source told the Daily Mirror newspaper: "Mischa was looking pretty merry in a bedraggled short flowery dress and white bow. She and Ali were all over each other backstage, and kept popping off to the toilets - presumably for a cheeky kiss.
"They just returned from a break in the South of France and things are obviously going really well."
Mischa - who has been linked with a string of famous men, including singers Luke Pritchard and Johnny Borrell - recently said she was looking for a new man.
She said: "I`m not even dating. I`m just on the prowl I suppose."
She also revealed how she has never been dumped and said the closest she had came to getting her heart broken was when a relationship ended mutually and she just got angry with the boyfriend for not letting her end the romance alone.
She said: "I`ve never been dumped. One tried to make it quite mutual though so that felt as close to dumping as I`ve got. I kind of lost it and was like, `You are not turning this on me. I dumped you first.`
"I felt like my heart was broken at the end of a couple of relationships but it wasn`t really."