The duo first sparked dating rumours after they were spotted having dinner together in Malibu in late November.
In early December, the rumoured couple was reportedly spotted indulging in PDA at Jenna Dewan-Tatum's 35th birthday. They were later seen having a night outing together.
The 23-year-old "Good For You" hitmaker was asked whether she's dating the One Direction member on the red carpet of the 2015 Billboard's Women in Music event, reported Entertainment Tonight.
"Oh my god! No," Selena said while laughing. "I love him, I always have. He's amazing," added the singer of Horan, 22.