There are multiple artists with this name:
1) Opus is an Austrian pop-rock group which was formed in 1973. In 1984 they released "Live Is Life" which topped the charts in many countries, and a live recording of the song even made the Top 40 in the USA in 1986. It remains popular as a sing-along song for crowds at sports events in Europe. A cover version was also performed by the Slovenian band, Laibach.
Opus is still active, but have not enjoyed the same success since "Live Is Life", and are generally considered a one-hit wonder. Read more on Last.fm