WordWeb Online

1. Easy in mind; not worried
   "the prisoner seems entirely unconcerned as to the outcome of the examination"
    
2. Not occupied or engaged with
   "readers unconcerned with style"
    
3. 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"

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

Antonym: concerned