Yes but it goes too mushy to be a risotto when you defrost it, as the rice in a good risotto is meant to be 'al dente' - with bite - to be really served at its best. You can get ready to cook stir fry rices or paellas anyway, but these don't rely on the best types of rice for the results...
Best suggestion is for any left over risotto, make up some small 'cakes', coat in breadcrumbs and freeze these (with a greaseproof paper between each cake so they aren't one big stack of frozen rice). No need to defrost before cooking and they will cook in about 6 - 7 mins in a little hot oil....they will still possibly be a little too soft if you have over cooked the rice in the first place, but they should be ok and are quite tasty.
Freezing affects the texture of food, so depending on what else you have in the risotto, some recipes will freeze better than others anyway.