The Whites will move above Sheffield Wednesday into the top six if they beat Blackburn at Craven Cottage on Tuesday.
Button, 28, who joined Fulham last summer from Brentford, told BBC London: "There's 10 games to go, nearly a quarter of a season.
"A lot of things can change so as confident as we are, we've got to make sure we maintain that."
Fulham are the Championship's in-form side, taking 17 points from their last seven games, including a 3-1 victory at leaders Newcastle on Saturday.
Reaching the play-offs would mark a dramatic turnaround in 15 months under head coach Slavisa Jokanovic after they finished 20th last season.
The former Watford manager transformed the squad ahead of his first full season, including bringing in Button - and the goalkeeper praised Jokanovic for his impact.
"The gaffer and his team know exactly what they want from us and drilled it into us from day one," he added.
"Why it's clicked recently I'm not too sure. Obviously there were a lot of changes in the summer, a lot of new faces.
"We're getting to know each other and we've shown on the pitch that it has come together."
Goalkeeper David Button says Fulham can not afford to be complacent as they target a Championship play-off place.