Yes. Fear is an appropriate response to something that is harmful and death is very harmful. In fact, if we believe in evolution we know that fear of such things that kill us, is the origin of fear. The next question -a question that needs to be separated from the first- is, how much time should we spend fearing death? Not that much. Just enough to motivate you to take steps postponing it. If we are cowering in dread – an understandable and justified response – we cannot make the most of your miserably short existence. After all, death is so dreadful, because life can be so good.