WordWeb Online

1. Not mindful or attentive
   "while thus unmindful of his steps he stumbled"
   - forgetful, mindless
    
2. (followed by 'to' or 'of') lacking conscious awareness of
   "not unmindful of the heavy responsibility"
   - oblivious

See also: amnesiac, amnesic, heedfulness, incognisant [Brit], incognizant, mindfulness, unaware, unmindfully, unmindfulness

Antonym: mindful