Is it dangerous to eat food accidentally cooked on polystyrene?

Possibly...: If the polystyrene has been designated microwave safe, then it most likely is safe. However, some forms of polystyrene break down more easily than others with heat, and toxins from the plastic might enter the food. If some other form of cooking than microwave was used that has a higher temperature (such as inadvertent cooking in a frying pan, grill, or oven) then i would not eat the food.