22-year-old German Sebastian Vettel is already under contract until the end of next year, but Australian Webber's contract is set to expire.
"He is driving extremely well," Horner said of the 32-year-old, "but the season is only half over so we are not in negotiations yet."
The Briton said both Vettel and Webber performed immaculately at Silverstone three weeks ago, confirming that "we have the strongest driver pairing in the field", according to Horner.
"Both drivers are highly focused and ambitious," he added.
Horner also believes Red Bull has the balance right in terms of how its drivers handle their relations with the public and media.
"In this respect I think Red Bull are better than anyone else," he claims. "Just look at McLaren. That's exactly how we don't want to handle our drivers."