They are learning to use their arms and trying to discover what they can do. At this point their control is not so refined yet so they can only wail their arms around and they are interested in making sounds. That's how they learn about cause and effect. My almost 1yo still likes to shake stuff and smack stuff together to make all sorts of noise!
Babies do lots of funny things at different stages! (: If she not in pain it's fine ...If you're worried or can tell she's uncomfortable then bring her to see a pediatrician