The group – who celebrate their 10th anniversary next month – put a countdown clock on their website, marking nine days until Friday October 19.
Girls Aloud are expected to perform on Strictly Come Dancing, where band member Kimberley Walsh is currently competing.
But the band, who formed on Popstars: The Rivals in 2002 and went on hiatus in 2009 to focus on individual projects, have not yet released details of how they will mark their return.
The online countdown comes after the five-piece are said to have teamed up to film a video for their new single, after recording the lyrics for the track separately.
Walsh, Nadine Coyle and Nicola Roberts recently watched Cheryl Cole perform a London date on her solo tour, A Million Lights, while fellow bandmate Sarah Harding was said to be in a studio recording solo material.
Cole has previously hinted that the Sound of The Underground singers will mark their 10th anniversary in November on "our birthday".
The former X Factor judge tweeted: "Today is a very good day to be a Girls Aloud Fan! "GirlsAloudAreBack".