How late is he going to bed? Night terrors are very common in some kids, and there is a research correlation found with being overtired.
With my older son, when he was taking a one hour nap and going to bed at 9:30pm (about 10.5-11 hours sleep total), he was having night terrors a LOT at that age.
I moved up his bedtime to 7:00pm, and his nap became optional, so he started getting about two hours more of sleep for 12+ total. The night terrors were gone.
Every time he goes to bed later than 8:00, he still wakes up with nightmares in the middle of the night. It is definitely related.
So try putting him to bed earlier and see if that helps. When he wakes up, is he able to speak or say anything?
Does he have any pain during the daytime? Earaches, anything like that? Could he be hungry?
I don't know if he is verbal yet, or how much you are able to find out, but I would try the sleep first, then also have him checked for ear infection, and lastly, make sure he has a good healthy snack (and tooth brushing) before bedtime.
L. Hamilton
http://www.theportablebaby.com