Abbreviation of the Latin phrase anno Domini, translated as “the year of the Lord.” Traditionally, it is used to date years after the birth of Jesus. Scholars and textbooks are increasingly using the abbreviations B.C.E. for “before the common era” and C.E. for “common era” to avoid using terms defined by their relation to Christianity. AP style, however, remains A.D. and B.C. Use A.D. preceding the year, as in A.D. 77. Do not say the seventh century A.D. If A.D. is not specified, it is assumed to be A.D. Use B.C. afterward, as in 255 B.C.
REFERENCE: Religion Stylebook