John the apostle defined “anti-Christ” as anybody who denies that Jesus is God in the flesh. (I John 4:2-3) That makes whole groups of people and even some religions “anti-Christ.” They were in the world then and they are in the world now! “many antichrists.” (1 John 2:​18)

Besides speaking of individuals who take such actions as being antichrists, they're also referred to collectively as “the antichrist.” (2 John 7) The antichrist first appeared in the time of the apostles and has been active ever since. Bible prophecy foretold just such a development. John understood the antichrist to be all who deliberately spread religious deception about Jesus Christ and Jesus’ teachings, religious deceptions.