The 3-0 Riverside Stadium win followed hot on the heels of a Boxing Day defeat of then leaders Burnley and a pre-Christmas victory at Millwall.
That lifted bubbling Boro to within six points of the play-offs - but Karanka did not see cause to celebrate.
The former Real Madrid defender said: "Of course I am happy, we had a good game and worked hard as a team - and we won again and we can enjoy that.
"But I am not getting carried away yet. It is important for a team to win two or three games in a row. It gives you momentum and moves you up the table.
"But if anyone thinks that gives us anything they are wrong. We have won nothing yet.
"I still want more from my team, from individuals and from the group. There is still room to improve.
"It shows that we are capable of winning games and playing well. Now we have to work harder to do that every game."
Reading boss Nigel Adkins said: "We have not been anywhere near good enough today. We can't hide from that fact.
"We started brightly but Middlesbrough countered well to score the first and I'm a bit disappointed with some of the decisions from the referee.
"Kaspars Gorkss has been sent off and I'm not sure the first was a booking and for the second he didn't even touch the player.
"Was there a foul in the build-up to the second? Maybe. And the penalty seemed a bit harsh too.
"But no excuses. We weren't good enough to be where we want to be and that is pushing for the Premier League. And fair play to Middlesbrough, they played well.
"We know we need to strengthen in January and we have had injuries but that performance was nowhere near good enough - and it's my responsibility to deal with it."