well according to babynamesword.com it means pleasing pleasant and is celtic in origin
http://www.babynamesworld.com/meaning_of_Africa.html
also from sacklunch.net through a jeeves search it says that africa has pheonecian origins
Meaning of Place Name: Africa
Africa: Origin traced to the Phenician "afer" (plural "afri"), "a black man," whence Latin, Africa, and Greek, Aphrike.
http://www.sacklunch.net/placenames/A/Africa.html