The Baggies have accepted an offer from the Championship for the central defender and is now thrashing out personal terms.
Villa have lost their opening two games this season - including an embarrassing 3-1 EFL Cup defeat to Luton on Wednesday - and boss Roberto Di Matteo confirmed he needs defensive reinforcements.
Ciaran Clark joined Newcastle for £5million and Joleon Lescott is unlikely to have a future under Di Matteo following relegation from the Premier League last season.
Chester has struggled for first-team opportunities at The Hawthorns since joining from Hull City for £8million last summer.