The Teessiders find themselves six points adrift of the Sky Bet Championship play-off spots following their 2-0 win at Blackpool on Saturday.
However, despite a run of four victories in their last five league games, Karanka is keeping his feet firmly on the ground ahead of Charlton's trip to the Riverside Stadium this weekend.
He told the Evening Gazette: "We have to think about the next game on Saturday because if we think we are a play-off team or a promotion team, it would be wrong.
"We need to improve our game still, we always need to be thinking about the next game only."
Boro have beaten Millwall, Burnley, Reading and the Tangerines, as well as earning a draw at Bolton, since their last league defeat at home to Brighton on December 14.