The former pundit has called for more from the Serbian front man.
Newcastle were among Europe’s biggest net spenders, shelling out around £47.7 million - according to the Mail - on five new arrivals and Keown feels that has represented good business on the whole for the Magpies.
"Newcastle fans love their passion but he needs to stay on the pitch! We’re only getting cameos with him so far and he needs to spend more time in front of goal rather than talking to referees.
"Georginio Wijnaldum scored that magnificent header on the opening day and Chancel Mbemba looks like he could become a good partner for Fabricio Coloccini."
Newcastle have endured a mixed start to the season and are yet to secure their first win but Steve McClaren’s men have already shown a marked improvement on the insipid displays that characterised much of last season.
The battling draw at Old Trafford has been the highlight so far and Keown believes the outlook on Tyneside is now positive once again, adding:
"The players Newcastle have brought in certainly look like they can improve this side and with several long-standing servants leaving the club it almost feels like a new era.
"They look better organised and more of a team this season but now they need to start scoring goals."
Scoring goals has been an issue, with just two managed in their first four games - and Mitrovic’s three-game ban won’t help matters.
The Serbian was brought in to be Newcastle’s leading man but has had a torrid time of it so far in terms of his disciplinary record and needs to get firing sooner rather than later if the Magpies are to enjoy a successful campaign.