The Guinea international opened the scoring for the hosts in the 34th minute.
Following an error by Thomas Delaney, the ex-Salzburg midfielder picked the ball and unleashed a fierce strike past Jiri Pavlenka. And with just two minutes left to play, Bernardo put the game beyond the visitors' reach with a second goal.
The strike was Keita’s first in nine German top-flight appearances so far this season.
Despite the win, Ralph Hasenhuttl’s side remains second in the German Bundesliga standings, three points behind leaders Bayern Munich.