The "Great Gatsby" star, 30, welcomed a daughter named Evelyn with her rocker husband Marcus Mumford in September, reported Contactmusic.
"Oh no. I think it's very important not to exercise for at least six weeks after you have a baby and I wouldn't want to push that. This (my figure) is just Spanx (control underwear) and breastfeeding," she said.
Mulligan said she found out she was pregnant during her stint on Broadway in a production of Skylight, and her first worry was about her costumes.