I do not have any clue about the origin of the name but I do know there was a Aphra Behn in England some centuries ago. She is the first professional female author we know of. Here are some links with the information we have on her: http://feminism.eserver.org/memoir-of-aphra-behn.txt
This one is particularly interesting as it offers some variants of the name, which might help to trace the etymology. http://en.wikipedia.org/wiki/Aphra_Behn