The Hammers, riding high again after finishing fifth last season, lost just two Premier League games in this campaign before defeat at Wolves at the end of last month.
They have dropped out of the top four after one league win in their last six, but Moyes, whose side take on Southampton at home on Boxing Day, appeared relatively unconcerned.
The 58-year-old Scot said: “I put it down to a fantastic start to the season that got us to fifth and got us fourth.
“We have been so good. It would have been very difficult probably to absolutely maintain that all the way.
“Clubs have dips at different times. Some teams started the season poorly and have picked up a bit now and some teams really started well and are having a little bit of a wobble.
“I think when you’ve played the amount of games (we have) and you’re asking the players to keep those levels up in every game, it can be really difficult.
“We’re a team trying to grow and build. We’ve probably had 18 months where we’ve had no real problems, so it wouldn’t be unusual if we had a little bit of up and down here and there.”
Since that 1-0 defeat at Wolves in November, Moyes’ side have lost at Manchester City and Arsenal, and dropped more league points against Brighton and Burnley, albeit with a victory against Chelsea in between.
Moyes said: “Players through the season will have periods where they’re right on top and full of confidence and periods where they’re not quite as good.
“You have to try and manage them through, help them through it and we’re no different from anybody else.
“We’re going to go through that like all the clubs do. But for us to keep consistent is really important and hang in around the top as long as we can.”
The Hammers were hovering above the relegation zone when Moyes returned for his second spell in charge at the end of 2019 and exceeded all expectation last season by securing European football.
Moyes added: “It’s great that I’m not talking about trying to stay out of the bottom three because that’s really been the talk at West Ham for a lot of time.
“We’ve changed it very quickly and we’re really enjoying the thought of being up around the top clubs.”