not a good idea, rice can make you very ill, you wouldnt be able to cook it from frozen, you'd have to de-frost it, this should never be forced ie in a microwave/running hot water over it,
but, rice is very suseptable to food poisoning bacteria, you cant make it safe..
youd be best not freezing it or reheating it at all,
but if you do, make sure it is very very hot add salt and boil it for a while.. but then you still risk getting ill..
brown rice takes a long time to cook in the first place, but then cooking from frozen to eating, would take a long time too.. there doesnt really seem much point freezing it in the first place??