This is a local custom, that is mostly practised in Austria, but I found also the masks in Switzerland. The masks are worn to chase the winter-ghosts. They are worn in february to allow the spring to finally come, when the dark winterghosts are gone. But to chase a winterghost, you have to to look furious and ferocios--- more than them.
There are many legends ranking around the klabeif... in our times now they come with St Niclaus. But the custom in itself is very ols, in fact it is pre-christianism.
Have fun while watching the Klaubeif and feel the soft shudder running up your neck.