The 27-year-old has recently been linked with a move away from the Premier League side.
Johnson said: “I’m looking forward to going forward with Birmingham.
“I have enjoyed it here and I am still enjoying every minute of it now.
“Moments like last weekend at Wembley were the reason why I came here.
“Now another big plus point in anyone’s career will be playing in Europe. We will enjoy that when it comes around.”
Johnson added: “I knew the club was going in the right direction and, yes, I’m happy here.
“Until the manager wants me gone, then I’m here.”