Having earlier today listed Call of Duty: Ghosts UK supermarket chain Tesco have also put up a page for an 'Upcoming Halo' on their website.
The retailer has given the title a holding date of 31/12/13, Halo 4 – the last entry in the Halo series – launched in November 2012 and all games in the series have either been released in September or November with the exception of Halo Wars which was released in March. The listing currently shows generic Xbox 360 box art.
Speaking to GameSpot a Microsoft representative commented that the listing is "not indicative of a Halo product launch."
Developer 343 Industries have already confirmed that they're working on Halo 5 and Halo 6 as part of the 'Reclaimer Trilogy' started with Halo 4. However, the next entry in the series could be a spin-off such as Halo 3: ODST or a remake like Halo: Combat Evolved Anniversary.
Microsoft have launched a Halo game every year since 2009; Halo Wars and Halo 3: ODST (2009), Halo: Reach (2010), Halo: Combat Evolved Anniversary (2011) and Halo 4 (2012).
The 343 Industries team is looking to employ developers with MMO experience among others.