The Spain international has scored seven goals in four games since signing for £32m from Atletico Madrid in the summer, and was awarded the Player of the Month gong for August.
Keown told the Daily Mail: "He's a mixture of Dennis Bergkamp's touch and Didier Drogba's strength and presence.
"He can have a tear-up or score the perfect goal and that is unusual. He has anticipation, hunger and doesn't mind scoring scruffy goals.
"Every defender in the Premier League should be relishing the prospect of facing Costa."
Manchester City host Chelsea on Sunday.