absent-minded

Absent-mindedness can refer to three very different things: 1) a low level of attention ("blanking" or “zoning out”); 2) intense attention to a single object of focus (hyperfocus) that makes us oblivious to events around us (See absent-minded professor); or 3) unwarranted distraction of attention from the object of focus by irrelevant thoughts or environmental events.
See more at Wikipedia.org...

(a.)
Absent in mind; abstracted; preoccupied.
  

forgetful Our neighbor is very absent-minded and is always getting locked out of his house.

adj.
کھويا ہوا , گم , غوطہ ميں , پراگندہ دماغ

Synonyms and related words:
Lethean, absent, absorbed, abstracted, amnestic, bemused, blocked, castle-building, converted, daydreaming, daydreamy, distracted, distrait, dreaming, dreamy, drowsing, ecstatic, elsewhere, engrossed, faraway, forgetful, forgetting, half-awake, heedless, in a reverie, in a trance, in the clouds, inadvertent, inattentive, inclined to forget, lost, lost in thought, meditative, mooning, moonraking, museful, musing, napping, nodding, oblivious, off, pensive, pipe-dreaming, preoccupied, rapt, repressed, somewhere else, stargazing, suppressed, taken up, transported, unaware, unconscious, unheedful, unheeding, unmindful, unnoticing, unobserving, unperceiving, unseeing, withdrawn, woolgathering, wrapped in thought