There is more than one artist with this name.
1) Actarus was a post/math-rock band from Luxembourg. Formed in 2002, the band released one full length, one EP, and a split-cd with fellow Luxembourg band "Eyston." The group disbanded in 2004, with members forming or joining bands such as "Do Androids Dream of Electric Sheep?", "Artaban," and "Miaow Miaow."
2) Actarus was a '70s group from Italy, famous for their opening and closing themes of the anime UFO Robot Grendizer. Read more on Last.fm