According to its ESRB (Entertainment Software Ratings Board) rating,
Resident Evil 6 will be the first Resident Evil to have nudity. It will be rated M for Mature, as all previous games in the series, but now there is a little skin to go along with the blood, gore, and intense violence.
The ESRB's description of the mature content reads: "One female boss character (a human-spider hybrid) is depicted nude—though without any discernible details (i.e., no nipples or genitalia); during one attack move, she briefly caresses her breasts while straddling on players' character."