The striker scored in the 2-0 FA Cup win over Bournemouth on Saturday.
The striker has enjoyed an impressive campaign for the Blues so far this season, with 21 goals in all competitions so far, 16 of which have come in the Premier League.
He managed his 21st in the FA Cup win over Bournemouth on Saturday afternoon, ending what has been a disappointing couple of weeks for him.
And Keown has now urged him to show more passion in games to add more to his tally, saying at times he can look like a pussycat.
"Lukaku has got to demand the ball more at times,” he told BBC Sport.
“He has to show passion - he doesn't seem that bothered. He's a bit like a pussycat, you've got to get him angry to get him playing."
The Blues will now be hoping they can get Lukaku to add more to his tally in the remaining games of this season.
They are currently 11th in the table after a disappointing campaign, but only five points outside of the top six, meaning a place in Europe is still a possibility.
If they were to secure that, they would an impressive run and Lukaku firing on all cylinders as he was in the earlier parts of this campaign.