The Canaries fell to a 1-0 defeat to Stoke City on Saturday which dragged them back into the fight at the bottom of the table.
Howson told the club's official website: "It's in our hands. If you start worrying about what other teams have done, that could be the problem because you're relying on other people. We just need to concentrate on ourselves."
Norwich are 14th in the Premier League and are six points clear of the relegation zone with three games to play this season.