It is very normal for all children to have specific fears at some point in their childhood. Even the bravest of hearts beat right up against their edges sometimes. As your child learns more about the world, some things will become more confusing and frightening. This is nothing at all to worry about and these fears will usually disappear on their own as your child grows and expands his or her experience.
In the meantime, as the parent who is often called on to ease the worried mind of your small person, it can be helpful to know that most children at certain ages will become scared of particular things.