"Don't worry, be happy!"
Translation:Ikke bekymre deg, vær glad!
"Bekymre" is a command/imperative here. Those almost never end in R (vær is an exception!). "Ikke" is the most common way to begin a negative imperative, just like "Don't... !" in English. You can also switch "ikke" and the verb, but it sounds a little strange to me that way.