The 'Imitation Game' actress is reportedly expecting her first child with husband James Righton - who she married in May 2013 - and is already past the first trimester, "multiple" sources told the New York Post newspaper's Page Six magazine.
Keira, 29, sparked speculation she was pregnant at the Moët British Independent Spirit Awards on Sunday when she stepped out in an embroidered and billowy dress much different to her usual fitted style and appeared to stay away from alcohol.
The 'Atonement' star has previously admitted she wants to have children but insisted she would never give up her career to raise a family.
Speaking last year, she said: "Would I want to be a stay-at-home mother? No. On the other hand, you should be allowed to do that, as should men, without being sneered at."
There was more good news for Keira yesterday after she was nominated for the Outstanding Female Actor in a Supporting Role Screen Actors Guild (SAG) award and she said she was "honoured" to be up for both that award - which she will contest with Meryl Streep, Patricia Arquette, Emma Stone and Naomi Watts - and Outstanding Performance by a Cast in a Motion Picture with her castmates.
She said: "Thank you so much to the Screen Actors Guild. It's such an honour to be nominated by your peers and in the company of this group of talented women. I'm thrilled to celebrate this morning with Benedict Cumberbatch and the cast."