"Come on!" Cobie pleaded when ET's Nischelle Turner whipped out the racy cover, which hits newsstands April 21.
The 33-year-old mother was slightly embarrassed by the attention at first, but explained that she wants to savor these moments, as they might not be around forever.
"I'm getting to an age where pretty soon people are not going to want to see me topless, so I should cash in on that now," Cobie said. "So I just went for it."
Her red carpet dress also turned heads, opting for a strapless, blue Bibhu Mohapatra creation.
In the movie, opening May 1, Chris Hemsworth (Thor) reunites with Robert Downey Jr. (Iron Man), Scarlett Johansson (Black Widow), Mark Ruffalo (Hulk), Chris Evans (Captain America), Jeremy Renner (Hawkeye) and Cobie (Agent Maria Hill) for the film, which follows Earth's mightiest heroes as they battle to save the planet from destruction at the hands of Ultron (James Spader). Samuel L. Jackson (Nick Fury), Don Cheadle (War Machine) and Anthony Mackie (Falcon) are also among the familiar faces.