Klaas-Jan Huntelaar's brace saw Schalke to the come-from-behind win at the SGL Arena in Augsburg on Friday.
Back-to-back victories have helped Schalke consolidate their spot in the Bundesliga's top four and Keller wants his side to keep improving.
"We can feel slightly more satisfied now when looking at the table. Two months ago, nobody would have thought we'd be where we are now," he said.
"We also know we can't afford to rest on our laurels now."
Augsburg took a shock fifth-minute lead through Tobias Werner, who capitalised on a defensive mistake to finish clinically into the bottom corner in a one-on-one with Ralf Fahrmann.
The visitors levelled in the 33rd minute as Augsburg goalkeeper Alex Manninger palmed a Kevin-Prince Boateng strike into a dangerous area, and Huntelaar was on hand to tap in.
The prolific Dutchman's second – on 49 minutes – was even easier as he tapped a Sead Kolasinac cutback into an open goal.
Keller said his team struggled to settle away from home and rated them as 'poor' early on.
"It was a hard-fought win. It's never good to fall behind after just five minutes. Augsburg started well, whereas we hadn't settled yet," he said.
"We weren't moving well, weren't distributing the ball well and were generally playing poor football. The equaliser came at the right time."
Augsburg coach Markus Weinzierl, whose team sit sixth, was pleased with his side's display and believes Schalke's individuals made the difference.
"It's a bitter defeat but I think we put in a very good performance," Weinzierl said.
"Ultimately though, we've got to be rewarded for those efforts after 90 minutes but we didn't have the luck we needed to score an equaliser in the closing stages.
"Conceding the equaliser in the 33rd minute was frustrating. After a good start, that goal really put us off our stride, but we found our way back into the game.
"Despite the defeat, our performance will give us greater confidence, because we fought well. At the end of the day, the individual class of the Schalke players was the deciding factor."
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