one possibility would be a vitreous "floater". the eye is filled with a jelly-like substance so small specks can form in the visual field. because there can be other possibilities and because your eyesight is important i would encourage you to see a good optometrist or ophthalmologist for a thorough eye examination. in the meantime you can read about "floaters" by doing an internet search.
black spot in right eye when looking at computer screen and in sunlight-2 months now. should i be concerned?