It was announced on the final episode of K-ON!! that a feature film is on the works. It was later on announced in their official website. Asami Sanada, who voices Sawako Sanada in the said series is surprised that there would be a feature film as stated in her Twitter account.
Source: ANN
As a fan of K-ON!, I am excited about the upcoming film. Hope this would be about their dream to perform in Budokan! I really needed to catch up with the second season.