Is this person someone you know? If you answered yes to that question then this means that you are probably angry with this person in life. If you are already obviously already angry with this person and well aware of this fact, then the fact that you are dreaming about it means that you are still very much at odds with this person and still angry over whatever event it was that caused you to be angry with this person in the first place. You clearly have some unresolved issues, so you should ask how they feel.
This is the best way to make sure that you do not go on holding a grudge for no reason. If they have done something purposefully to wrong you, try to get over it, but unless you know it for a fact then it could be an accident or a simple misunderstanding. They may not know that they hurt your feelings, so you should make them aware of that fact and give them the opportunity to apologize before you make assumptions.
When you have a dream that you are in anger with someone but you do not harbor any feelings of anger towards the person in the dream in your waking life, what this signifies is that you are subconsciously angry with them. Maybe it is something in their manner or the way they carry themselves. Maybe they annoy you in a way that you are not even consciously aware of. But whatever the reason you are fixated on them and how they annoy you, so much so that you even dream about them at night. Try avoiding them, or try to spend more time with them to see why it really is that you are so angry with them.
When you have a dream that you are angry and it is towards no particular person, this usually just acts as an indicator of your mood recently. For someone that knows they have been unnecessarily angry for the past few weeks, this might be a sign that they need to slow down and stop treating others so badly. If you are unaware that you have been angry recently then this is a wakeup call. Our dreams are based on what is familiar to us, so if we have been in bad moods lately then we will have dreams that depict us in a bad mood. Even though you may not have realized it, now is your indication that you should stop and maybe go out and apologize to those that you may not have been fair to. You also might want to go out and get your blood pressure checked just for the heck of it to make sure that you’re not overly angry for a medical reason.