Water Hester leaks at times

I have noticed that my water heater will leak from the pressure relief outlet. Is is normal for this to happen on occasion. It is not a constant leak. For example. I opened one at a time a hot waters spigot in the camper and nothing leaked on the exterior pressure relief. Finally some water would come out after running enough water. It does stop. Not a lot of water but enough to see in the bottom of the lip behind the outside water heather access panel. It will do it this sporadically. Never constant and never a puddle of water overflowing down the side of the camper. Tks