Is this mould on a filter?

I can't get blow this off like dust, I'm wondering if its mould? This filter has spent the last few months in the plastic case it came with.
If it is mould, what is the best way to stop it spreading and to store the filter in the future?
I have uploaded images of the filter with annotated places where the possible mould is.
Images of the filter

Thanks for your help,
Izaak