Rosberg, 30, will be out of contract at the end of the season and is now in his seventh season with Mercedes, having joined the current champions in 2010 after they took over the Brawn team.
Wolff said the fact a new contract had yet to be agreed would not be a distraction for the team or driver as they fight for the title, and there was no hurdle delaying completion.
"It is not a type of instability as we would like to continue in the same way with Nico as we did," the Austrian told reporters at the Canadian Grand Prix.
"It is down to the detail in the contract. It is pretty normal negotiations. We are not flirting somewhere else and he is not flirting somewhere else, that is why it is not a distraction."
Rosberg won the last three races of 2015 and first four of this season. However he has not been on the podium in the last two grands prix, and saw his overall lead shrink to 24 points ahead of Montreal.
Triple world champion Lewis Hamilton, who has beaten Rosberg to the last two titles, agreed a new deal last year and has a contract till the end of 2018.
Hamilton's contract negotiations were similarly protracted.
(Editing by Alan Baldwin)
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