The German international, who joined the Gunners in 2011 from Werder Bremen, still has 18 months left to run on his current deal.
However, the 29-year-old has conceded that he is "pleased" to have begun talks over an extension to those terms.
"I am very delighted here. The first year was tough for me, a very tough challenge, but the club and the manager always trusted me in a special way. I think it is a little reward that we are talking [about a new contract], because I still have one-and-a-half years left," the London Evening Standard quotes Mertesacker as saying.
"There is no rush but it seems that some people are delighted with my performances at the moment. I am pleased with the situation."
Mertesacker has made 18 appearances in all competitions so far this season.