Frank believes his side are now playing for the second automatic-promotion spot, with the likes of Watford and Swansea breathing down their necks.
"Congratulations to Norwich, I think they are 100 per cent certain to be promoted," he said. "That is not mind games or anything like that, it's based on the quality of their performances this season.
"They are now 10 points clear, they have the same team who won promotion two years ago, no injuries and have an excellent coach in Daniel (Farke).
"They are a very good side and it wouldn't surprise me if they went undefeated for the rest of the season."
Frank was disappointed with his side's display at Carrow Road.
Sergi Canos missed an early chance and there was some late pressure at the death, with a penalty appeal being turned down, but the Brentford boss had no complaints about the result.
"It was a tight game between two good teams but Norwich deserved to win because they created more chances than us," he said.
"Our performance might have been good enough against many teams in this league but not the number-one team. I am disappointed that we could not produce our best against them.
"We needed to be better on the ball and in our decision making and needed to create more.
"We might have had a penalty near the end when Bryan Mbeumo went down but it was only a 50/50 one and it went their way.
"We have to remember that we are still in a good position - we just have to put this behind us and get ready for Rotherham at the weekend."
Additional reporting by PA.