The Scot has been linked with Celtic in recent days.
But Keen told the Albion website: "Since Christmas, Graham's played a lot of games for us," he said.
"Perhaps he didn't get the goal return he would have hoped for. But, like Markus [Rosenberg] in training, his finishing is absolutely top draw.
"Maybe the goal today will give him a little bit of impetus.
"After Christmas, he had a big role in the squad and the way we played. He put in some good performances.
"Can he go a little bit further and do a little bit more? I think he can - certainly in terms of scoring and creating goals."