The 25-year-old, who plays the shared girlfriend of Chon (Taylor Kitsch) and Ben (Aaron Johnson), was shocked because mostly women strip down for such scenes.
"When you are not doing nudity, you just assume that the boys aren't either, because it's normally the woman that's naked. But in this movie you show up and the boys are naked! Which was actually a refreshing thing. But they did look very handsome," okmagazine.com quoted Lively as saying.
The actress feels it is important to be comfortable with co-stars during love making scenes.
"Our first day was the love scenes. If you don't feel comfortable with these people after that, you're never going to feel comfortable with them," she said.