I encountered this song (individual track, track as part of entire soundtrack compilation), titled "Muru Muru's Melodrama", in an OST of Mirai Nikki, and I wonder when it was played. I've tried to listen as carefully as I could, but I couldn't find that BGM anywhere, neither in the original series nor in the OVA.
It appears in a couple of the 'Mur Mur-Sensei's Future Diary Behind the Scenes' short specials that appear at the end of each episode after the credits. In particular, I have noticed this track in this section on episodes 11 and 16.
Depending on what version of Mirai Nikki you are watching, you may or may not get this extra section at the end of the episode, I think that it may only be included in BD versions of the anime.