Arsenal have lost four of their opening seven Premier League games, with Mertesacker coming in for criticism for some of his performances.
"Arsenal is one of the top teams in the world and the level of the league in general is very high," the defender said.
"But it is clear that mistakes happen. They are almost inevitable in a team which has not yet gelled."
Mertesacker is boosted by the faith Wenger has in his team, though.
"The coach has been the pride of Arsenal for years," he said. "Arsene Wenger does not sign players about whom he is not totally convinced. He gives this feeling to everyone on a daily basis. This knowledge gives me a lot of security.
"He (Wenger) has a huge reputation there and enjoys complete confidence.
"For the Arsenal fans Wenger is a hero and he cannot lose this status. There is no one here who is not certain that the success will return. We have a talented team with a lot of potential lying dormant within us and it's only a matter of time before that comes to the surface."