There could be several reasons for this and it's often difficult to pinpoint the precise cause. Brown, dead spots on leaves are usually scorching, a sign that your plant is getting too much light. If this is not the case, look towards watering. Brown spots can also be due to a lack of watering. Fungus can be a cause as well, but this is more prevalent in overly moist plants. Do you fertilize it regularly? It may be that the salt from the fertilizer has built up and the plant is getting a bit sick from it. Try repotting it with some fresh soil. While you are doing that, just check for root rot too. This is the less common reason for spotting on this plant.
Here is an article on caring for rubber tree plants that you may find helpful: https://www.gardeningknowhow.com/houseplants/rubber-tree/how-to-care-for-a-rubber-tree-plant.htm