According to the outlet, Mara is five months along.
The "House of Cards" star and Bell, 32, started dating after they met on the sets of 2015 superhero drama "Fantastic Four".
The couple confirmed their engagement in January 2017 and later that year, they tied the knot in a Los Angeles ceremony.
Bell was previously married to "Westworld" star Evan Rachel Wood from 2012 to 2014 and the two share a son, who was born in 2013.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)