I suspect that it is brown leaf spot fungus so if it is any disease tht spreads then take off effected leaves. But with ficus if you take too many of the leaves off then it may die so get a fungicide would be my opinion if it has spreaded to most leaves. Oh and if it is the leaf spot fungus then stop misting.
That, or, more likely, you have spider mite in your plant. THese are tiny, and cause white and brown spots on the leaves.
Just as an FYI.. You can completely defoliate ficus without any problems.