The loan runs until 3 January 2015 inclusive. The terms of the deal mean that Blues have an instant recall on Bell if needed and he is also eligible to play for Blues in non-first team matches if required (e.g. U21 matches).
It is the 20-year-old left-back's fourth loan spell.
To date Bell has one Blues first team appearance to his name. That came in the 2-1 Sky Bet Championship defeat against Leicester City in January 2014 at St. Andrew's.
Paul Cox's Mansfield Town side finished last season's League Two campaign in 11th spot.