The couple, who keep their relationship out of the limelight, are "over the moon" about becoming parents, according to People magazine.
"They literally could not be more excited," a source told the publication. "She's feeling great."
Ryan Gosling and Eva Mendes have been together since 2011
Eva was photographed on Wednesday, although her bump wasn't visible due to the large number of bags she was carrying. The Hitch actress is thought to be seven months pregnant meaning that the couple, who have been dating since 2011 after meeting on the set of The Place Beyond The Pines, will become first-time parents at the end of the summer.
Ryan, 33, and Eva have always been very discreet about their relationship and are yet to be photographed together this year.