Mostert was promoted to the Bears' 53-man roster Wednesday, Scott Krinch of CSNChicago.com reports.
Mostert has appeared in 11 NFL regular season games with three teams after going undrafted in 2015. He has yet to record a rushing attempt, however, instead spending all of his time as a kick returner. He'll fill in the No. 4 spot at running back in Chicago behind Jeremy Langford, Ka'Deem Carey (hamstring) and Jordan Howard.