The 26-year-old actress was snapped running with rumoured boyfriend Sean Penn in Malibu on Sunday with what appeared to be a baby bump underneath her T-shirt.
But a spokesman for Scarlett – who split with husband Ryan Reynolds last year – denied that the star is carrying a baby.
'Scarlett is not pregnant. She's outside running and it's simply the placement of her shirt that is misleading,' the rep told Us Magazine.
'She's been training for The Avengers for over four months and is in the best shape of her life.'
Penn and Johansson have reportedly been dating since early this year.