The 20-year-old has started the last two games amid an injury and suspension crisis, which left the manager looking at loan signings and marked his first home start in the Sky Bet Championship with the equaliser in Tuesday night's 1-1 draw with Huddersfield.
Mowbray told the club's official website: "I'm delighted for Ben. He's a fantastic personality and is a really driven guy from this part of the world.
"A lot of people are asking me about loans and who we are going to bring in. He's been out on loan several times because he's so desperate to play.
"Why would I want to get a 20-year-old from the Premier League on loan when I've got Ben Gibson here bursting out of his shirt to play for the Boro? I want to give him an opportunity.
"It's sometimes too easy to go out and pluck a Johnny Average from some team who hasn't played for months when you've got a player like Ben Gibson in your ranks bursting out of his shirt and knocking on my door every second day to say give me a chance."