The couple appear together in Derek Cianfrance's upcoming crime drama "The Place Beyond The Pines", which also stars Bradley Cooper, Rose Byrne and Ray Liotta, reported Marie Claire magazine.
"He's your dream co-star. I have never felt so creatively satisfied on a film," said Mendes.
Quizzed on her romantic relationship with the "Drive" star, Mendes said, "Stop, just stop! I'm not gonna budge. I feel uncomfortable talking about it. It's too personal."
Asked whether she wanted marriage and children, the 38-year-old said, "Those are such boring topics to me."
"I don't like talking about things that I want in the future, because I feel by verbalising things, they won't come true," she added.