The Gunners finished a successful pre-season on Saturday with a comprehensive 3-1 win over Manchester City in Helsinki.
"I think it was a long pre-season but we did well, especially in this game against Man City," Mertesacker told the club's official website.
"That was a good finish and I think we're well prepared for the season. We have now international duty which makes it a bit difficult but I think when we come back on Thursday, we will completely focus on Aston Villa."
Arsenal start the new campaign at home to Villa on Saturday.