Is it normal to have minimal mucus in throat. 1 year post throat cancer and radiation therapy? Did the radiation cause the mucus?

Yes. Radiation therapy can cause dry mouth resulting in thick mucous secretions. Talk to your radiation doctor if a medicine to increase saliva production, mouth rinses, or possibly even accupuncture could help.
Very common. It is very common to have little mucus in your throat or dryness. This is a side effect from the radiation and it takes a very long time to get better. It may actually not go fully back to normal. Many patients carry bottles of water all the time to keep their mouths well hydrated and fight the dryness. Best wishes, ariel.