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

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