1 John 2
18 Little children, it is the last time: and as ye have heard that antichrist shall come, even now are there many antichrists; whereby we know that it is the last time.
19 They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us.
The antichrist and other antichrists were already around when John wrote his epistle.
John was a Hebrew; therefore, it is probable that the "us" John refers to in 1 John 2:19 is likely His brethren that followed Jesus.
1 John 4
6 We are of God: he that knoweth God heareth us; he that is not of God heareth not us. Hereby know we the spirit of truth, and the spirit of error.
The "spirit of antichrist" is equated to a "spirit of error". The antichrist represents an error - false teaching - that was (and IS) being spread.
Antichrist = erroneous doctrine. Antichrist primarily represents a set of false teachings, not simply some future possible world religious/political figure, or something inserted under the skin. Those accepting the error promoted by the "spirit of error" or "spirit of antichrist" are unintentional victims of the spirit of antichrist.
So, the "antichrist" was (and is) a doctrine or set of doctrines that were already being spread in the latter part of the first century as false teachers betrayed the truth.
However there will be one individual, who has many, many names in Scripture but who is commonly known as "Antichrist", who will come to power sometime in the future and control the world, control the world economy, and force every single person on the planet to take a mark swearing allegiance to him or they will not be able to conduct commerce.
That person has never existed in the history of the world.
That's why I have to laugh when someone tells me that the events of Revelation took place in 70AD. You have to discard most of Scripture in order to actually believe that.