Milner signed a four-year deal when he became Villa's Â£12million record signing after moving from Newcastle during the summer of 2008.
But O'Neill is keen to reward Milner for his superb form this season and also secure his services on a long-term basis.
Milner is a strong candidate to be part of the England World Cup squad after impressing Fabio Capello.
O'Neill confirmed: "I said to James couple of months ago that we would sit down in the summer about a new contract, regardless of whether he plays for England or not (at the World Cup).
"He is playing so well, it would be important that we do something if we can. By the time the summer arrives, he would be exactly halfway through his contract so it is not a bad time to do something.
"We will sit down in the summer, I said that way back before January. I said it to his agent. That is fine. They have never pushed or asked for anything and they are absolutely okay with that."