The Bosnian international has emerged as a crucial member of the Premier League-winning team since his £27m move from Wolfsburg in 2011.
Widespread reports have claimed that Dzeko, who set up David Silva's goal in yesterday's 2-0 victory over Newcastle United, will sign a new five-year deal.
"I'm very happy for him," Sky Sports News quotes Pellegrini as saying. "That's why he is renewing his contract here. He has a very important duty in our team, but I repeat, Edin finished last season playing the same way as he has started.
"I don't think it's 100% finished, but yes he will renew his contract. He's a very important player for us."