The 32-year-old singer was performing as part of her Keeper of the Flame tour, reported Us magazine.
She paired the black-and-white T-shirt with a pair of cut-off jean shorts and fishnet stockings.
Even though the couple have not spoken about their relationship to the media, in June, the "Vice" songstress posted a sweet shot of a romantic dinner with a caption: "Farm life #healthydinner #wine=grapes #red55winery #RedRedWine #chicken&rice&everythingnice #dayoff.