De Gea scooped the Golden Glove award for the first time after recording his 18th clean sheet of the season in Thursday's goalless draw at West Ham.
It added to De Gea's fourth Manchester United Player of the Year award he collected this month as Mourinho lauded the Spain international.
"David has been terrific," Mourinho said via MUTV. "But the Golden Glove is about the team and not about somebody analysing the goalkeeper, and deciding this is the best goalkeeper of the Premier League.
"It is about clean sheets and they are about the team. Obviously, we are all very happy for David and it is a great team achievement."
De Gea's shut-out performance against West Ham ensured he cannot be caught by Manchester City rival Ederson in the race for the Golden Glove.
Chelsea's Thibaut Courtois won the gong last season, with Edwin van der Sar the last United keeper to claim the Golden Glove in 2008-09.
De Gea - who has been linked with European champions Real Madrid - said: "It feels good, it is my first Golden Glove award.
"I am really happy for that. It means we defended well in this league, I am happy for me and happy for the team.
"It is for everyone, it is a team award, not just for the goalkeeper. It's good for me but I am also happy for the team."