The Spaniard has been linked with a move away from west London ever since Jose Mourinho took over earlier this summer.
Reports this month suggested the Spanish international, who has twice been voted Chelsea's player of the season, was offered to Manchester United as part of a bid for Wayne Rooney.
Chelsea moved to deny that by issuing a statement on their website and now look set to reward Mata for his efforts since he joined from Valencia in 2011 with a new deal.
The 25-year-old has three years left on his current contract, however the new deal will tie him down until 2018, and improve his wages by around £30,000 to £100,000-per-week.
Mata is set to hook up with his Chelsea team-mates for the first time in pre-season this weekend following his exploits with Spain at this summer's Confederations Cup, along with international colleagues Fernando Torres and Cesar Azpilicueta, as well as Brazilians Oscar and David Luiz.