Green mould (?) growth on the compost/soil.

Aargh in my brand new bed which has garlic, onions, carrots, parsnips and spring onions in it there is a light covering of green mould like stuff growing? It has been raining on and off for a few days but surely this shouldn't happen so quickly? Or could it be the compost that had it in it, it's all brand new too? the soil definately didn't show any signs of mould beforehand.
Should I just leave it or is there something I could do, it doesn't appear too wet and I don't know if it will get worse or what?