Tottenham enquired about the availability of the midfielder, who has not been able to hold down a place in the starting XI since Jose Mourinho's return to the club.
However, Villa-Boas said no such deal would be happening - echoing the view of Mourinho that Mata would not be going anywhere.
"Chelsea wouldn't sell to Tottenham in any way or form, as they think that we are title contenders,'' he said.
"Mata is a great, great player - player of the season last season - very, very important player for Chelsea.
"They're just not going to strengthen another team that, in their opinion, are rivals for the title.''
Villas-Boas is eyeing more signings as he prepared to lose Gareth Bale to Real Madrid - he admitted on Wednesday that deal "could happen very, very soon".
A move for Brazilian star Willian collapsed when Chelsea hijacked the deal last week.
Regardless of who comes in to replace Bale, Villas-Boas thinks Spurs will be well equipped for the year ahead given that they have won their first two games following a £60million summer spending spree.
"We have a very, very strong team the same. If this transfer (Bale) happens, it will give the opportunity to step up their game, step up the responsibility and I think we have seen that in the last couple of games,'' Villas-Boas said.
"There hasn't been any disruption. We've been working well and the team is training very, very well.''