Dier has 12 months left on his current contract in North London and will be available for free next summer.
The 26-year-old England international joined the Lilywhites from Portuguese outfit Sporting Lisbon in the summer of 2014 and has been deployed in a number of positions including defensive midfield and right-back as well central defense in his time at the club.
Dier has made 27 appearances in all competitions this season, underlying his importance to both Mauricio Pochettino and current boss Mourinho.
Ahead of Tottenham’s trip to Sheffield United in the Premier League on Thursday, Mourinho told reporters that the club are in discussions with Dier to tie him down on fresh terms.
Mourinho said: "My boss Mr Levy tells me that he wants Eric to sign a new contract and Eric tells me that he's more than happy here, more than happy with his situation, especially now that he feels we have a certain idea for him and the deal.
"And he tells me also that he wants very much to stay.
"So I hope that we can find an agreement because I'm trying to take the team in a certain direction and when I try to develop a player in the team it's because I'm waiting for a player to stay with us."
