What size are they and how large of a tank are they in? If they have been together for a while then it probaly will not stop, if they're relatively new together they might be setting up the pecking order of the tank. But yes they can be very territorial especially if they're both male. Depending on what size tank your keeping them having two oscars together is a hit or miss situation depending on each fishes individual temperment. Keeping two oscars will take a absolute bare minimum of a 90g tank but any fish that gets over 12" really should be in a 6ft. tank, unless they live alone then a 4ft. tank will do.
So with your fish if the other fish is getting hurt or not being allowed to eat then it's time to think about a tank divider temporary or rehoming the aggressor. Stress has a huge impact on fish and can lead to disease and death.
I have a breeding pair of oscars in a 150g long with each fish a little over 14" and they're days when I come home to soaking hardwood floors from them scrapping with each other.