The actress, known for jaw-dropping appearances on the red carpet, made a rare departure from her usual revealing style during a trip into town.
Without heavy make-up or a clinging dress, the 23-year-old looked almost girl-next-door in her ripped jeans and grey t-shirt.
Dressed-down: Megan Fox was spotted in Los Angeles yesterday looking casual and with barely any make-up in a departure from her usually glamorous look
She was accompanied by her boyfriend Brian Austin Green, 36, best known for his role in Beverly Hills 90210.
He co-ordinated with Megan's dressed-down look, also opting for a pair of jeans with a shirt and cap.
Fans of the actress will see a very different Megan in her new film Jennifer's Body, which opens in cinemas today.
She was joined by her boyfriend Brian Austin Green
She plays a man-eating demon who locks lips with co-star Amanda Seyfried and turns satanic after she is sacrificed by a band who sold their soul to the devil in order to get a record deal.
Fox, who plays the title role, explained: 'They think they are performing a virginal sacrifice but [Jennifer's] not a virgin, so it backfires and she gets inhabited by a demon.'
The gruesome film see the actress tearing men's bodies open and devouring their flesh.
Speaking about her lesbian kiss with Seyfried, she told Metro: 'There's lots of kissing everyone - boys and girls. This is a sexy one.'
The Transformers actress said that, in her opinion, girls can't be really be friends because they are essentially in competition with each other for attention.
She told the newspaper: 'Yes, girls are awful... because of the way society is set up - we're constantly in competition for male attention.
'Our fathers raise us wrong and we spend the rest of our lives searching for boys to pay attention to us, which validates us.
'So no girl can really be your friend, because if she takes attention from you, your daddy doesn't love you.'
Don't mess: She plays a man-eating demon in her new film, Jennifer's Body
