Ederson was at fault for Callum Hudson-Odoi's winner for Forest late in the game.
Guardiola said, "It is what it is.
"I never blame a player. I prefer to praise. I never blame. I didn't see the action but it's football. A good action from Hudson-Odoi so nothing to say."
City held 69 per cent of possession of the game and Guardiola also said: "It was a tight game.
"At the end it was one transition. We missed the pass, they did a transition and they scored the goal.
"We were a little bit slow in our process. We struggled to create chances but always we give credit to the opponent because they defended really well.
"We controlled the main threat, long balls to (Chris) Wood and second balls, really good, and after that the transitions always we were really good especially in the first half."