Naismith thinks that Everton must produce an instant response to keep their hopes of European qualification and FA Cup success alive.
The Scot told the club's official website: "It's a real disappointment and I think more so because we probably controlled the game for the first hour.
"After that Norwich probably went a bit more direct and the two boys up front caused us a few problems. As a team we are disappointed because of the kind of goals we lost. We've got a big week ahead of us now.
"We've just got to put this to one side and put on a professional performance on Tuesday. There's a routine the squad follows after games and it will just be a case of getting back on to that. We'll probably talk about the mistakes we've made and try to rectify that for the next game."
The Merseysiders face Oldham Athletic in a fifth-round replay on Tuesday before a Premier League clash with Reading next weekend.