Hitting back this morning at claims made by the Megaupload millionaire last week, Mr Key said the only person who cared about Dotcom was the man himself.
"The Government actually doesn't care about Kim Dotcom. He might think we get up every morning and it's a top-of-mind issue, but it's not," Mr Key said on TVNZ's Q+A today.
"In fact, most New Zealanders don't care about Kim Dotcom.
"The person who cares about Kim Dotcom is Kim Dotcom.
"And as we've said all the way along, if this guy believes he's so innocent, get on a plane, go to America and fight your case. If you win, come back to New Zealand no problem."
Dotcom claimed last week he had proof Mr Key had lied about his knowledge of the internet entrepreneur earlier than the day before the January raid on Dotcom's Coatesville mansion.
Dotcom is currently opposing an extradition attempt by the United States, which alleges massive breaches of copyright and money laundering in relation to Megaupload.
Mr Key said to lie means "you have to deliberately mislead people, and there's no way I've done that".
"He [Dotcom] is completely and factually incorrect," the Prime Minister said.
On the last episode of Q+A for the year, Mr Key denied criticism he had been "grumpy" and "tired" this year.
"When you work long hours, from time to time you're going to look tired," he said.
"I get off a plane and I start working. That's the way it works.
"I work a lot of hours and I have a lot of papers to read and a lot of things to deal with.
"Am I grumpy? Not in the slightest."
On the question of whether he will lead National to the 2014 election, Mr Key said: "I believe for sure I will be. I have the support of my caucus, unlike Labour."
