The Geordies currently have the best defence in all leagues in England in arguably the toughest competition - the Championship.
The England national team is under pressure to find fit and reliable keepers ahead of next year's World Cup as David James battles injury worries and Robert Green and Ben Foster have failed to fully impress Capello.
Newcastle boss Chris Hughton believes Capello should look at Harper as a potential answer due to his maturity and ability to make match-winning saves.
"It is the England manager's prerogative to look at all English keepers. He has to pick who he wants but if I look at Steve Harper's performances for us, I don't think there are so many better than him," said Hughton.
"Steve is proving what a good keeper he is. He has shown is that we are a team that is four points clear of second spot and ten points clear of third but what we have still needed is quality saves at vital times. Without him, we might not have that.
"He is a goalkeeper that has matured, and I think he is at his prime at this particular moment, and the types of saves he is making are not easy ones.
"He has made all sorts of saved, generally reflex saves, and of course that all stems from being at the right place at the right time. "We are certainly very grateful, even going back to the Sheffield United game when he made an outstanding save that enabled us to get the win.
"I think he is in top form at the moment. I think he is a goalkeeper who has been such great value to us and certainly we would not have the amount of points we have at the moment, if it was not for him."