According to NewType magazine, a four-frame manga "K-ON! (Keion!)" will be animated. The airing schedule and the production info were not given.
K-ON! has been published in Manga Time Kirara
magazine since May 2007. It's about four high school girls who are trying to revive a light music club, which was about to be closed.
Note: K-ON stands for Kei (light) Ongaku (music).
Source: Scan of New Type magazine
The manga author's website
Edited on Dec 26th=======================
Megami magazine published the character design.
Scan of Megami magazine
The production company has not been announced yet.
Edited on Dec 27th========================
The official website opened.
K-ON! Official Website