What Does Mejia Mean In Spanish?

It means Messiah not my daughter or my son.  It is listed by the Catholic church as a new family name given to converts from Judaism to Catholicism during Queen Isabella's reign.  The Roman Catholic Inquisition brought about the expulsion of the Jews refusing to convert.

Mejia is a surname of spanish origin. The first Mejia family had the origin in the region of Galicia (Northern Spain), extending rapidly to others regions and to Mexico and other parts of America. It is the 517 in the ranking of the most popular surnames in Spain and it doesn't have any meaning in spanish.
Similar surnames are Mejías and also Mexía.
Hope that it helps.