The Baggies reached the 40 point mark - generally regarded as the accustomed Premier League safety target - via back-to-back wins over Liverpool and Sunderland.
But Foster bristles at the suggestion Albion will now ease up and slip into a comfort zone.
Foster said: "Nobody here is treating the rest of the season as a holiday just because we're nearly safe.
"I think people were starting to think (before the two wins) that we'd switched off and that we were going to coast to the end of the season.
"That hurt us to be truthful because that isn't the way that this team is. The bunch of lads we have are not like that."
Foster added: "We are as hungry to win games now as we were back in August. We go into games wanting desperately to win.
"We want to build on the great start we had and finish as high up in the table as we possibly can."