Is this a lasting pain or simply one that occurs when the weight is set down after a set?
Some discomfort is actually normal, especially with straight bar curls (which is why I usually with the EZ bar for those exercises). Lesson one, your bones are not rigid steel beams. They are strong, however, they can also bend a little. When you curl a weight that is significantly heavy, your bones in your forearms bend slightly. No, that doesn't mean they are going to break because it would take more direct blunt force to do this.
When the bone bends, as soon as you set the bar down, those bones return to their normal shape. They ahve a certain level of elasticity, however, since this is still about force applied, the discomfort you feel is as they return to normal.
Over time, your bones will get even stronger if you continue to lift and this sensation may decrease.
Using the EZ bar instead of a straight bar may help to decrease this further simply because your arm is slightly rotated allowing force to be applied over two bones at once instead of each absorbing force more independently.
Bottom line, drink milk.