WordWeb Online

1. Lacking in interest, care or feeling
   "the average American...is unconcerned that his or her plight is the result of a complex of personal and economic and governmental actions...beyond the normal citizen's comprehension and control"; "blithely unconcerned about his friend's plight"
    
2. Easy in mind; not worried
   "the prisoner seems entirely unconcerned as to the outcome of the examination"
    
3. Not occupied or engaged with
   "readers unconcerned with style"

See also: blasé, blithe, careless, casual, cavalier, dégagé, detached, indifferent, insouciant, nonchalant, uninvolved, untroubled

Antonym: concerned