K-ON!! Official Band Yarouyo!! ~Let's MUSIC!! 4~ (「けいおん!!」オフィシャル 「バンドやろーよ!! 〜Let's MUSIC!!4〜」, K-ON!! Official Band Yarouyo!! ~Let's MUSIC!! 4~) is a collective album of the band Ho-Kago Tea Time, containing various "TV size" version of previous songs and also six instrumental versions of the song GO! GO! MANIAC.
The featured songs are sung by Yui Hirasawa's and Mio Akiyama's respective voice actresses Aki Toyosaki and Yōko Hikasa. The album was released on the 15th of June 2011 in Japan by Pony Canyon.