Go to admin console and navigate to users page and on the top there will be radio buttons to check active and inactive In the search bar type the user you want to check if not there in active list check in inactive list
if you want to make inactive acc to active by selecting the user
the scenario is am sending email to group before sending an email to group i have to check whether all users are active or not, if i include deactivated users the process module will fail in production. so need to remove the deactivated users