Rosemary With Powdery Leaves

We are keeping a rosemary plant indoors. Some of the lower leaves/needles have a white powder on them. We're pretty sure that it hasn't fallen from somewhere. Is there a problem with our plant or is this something normal that would be blown away by the wind if the plant were outdoors.

The plant might be suffering from powdery mildew. To combat that, tape some newspapers over the soil, then swish the plant a few times upside down in a solution of dishwash detergent about double the strength you would use for dishes. Repeat daily at least three days until all signs of powder are gone.
If the number of powdery leaves is not increasing, then it might simply be that the old leaves that are adapted to moister outside conditions are drying out prior to dying and are therefore shedding their stiff cuticle. The new leaves would then be OK.