Dreaming of someone you don’t recognize can be a clue to someone you are about to meet. Depending on what you did together in the dream, pieces of the puzzle will come together. It could be a person that you find yourself falling in love with, or a new friend outside the circle of friends that you have thought long and hard of abandoning.
On the negative side, it could be a stalker you are unaware of but have seen before and now are subconsciously recalling seeing them from a distance multiple times.