The Australian singer, who was recently announced as the new host of revamped Young Talent Time, was reportedly spotted cosying up to former Neighbours actress McIntosh during a trip to Maui.
One onlooker told the Herald Sun that they "looked like a pair in love", but a spokesperson for Mills has insisted that they are just friends.
The Network Ten representative said: "Rob and Stephanie are great mates, and have been for years. They both attended the same wedding in Maui."
Mills was once romantically linked to hotel heiress and reality TV star Paris Hilton, while McIntosh previously dated sports star Nick Riewoldt and Melbourne Rebels rugby player Danny Cipriani.
Cipriani later went on to have a long-term relationship with model Kelly Brook and more recently split from Australian swimwear model Lara Bingle. He was believed to be dating Katie Price, although she denied the reports last month.