"And this is that spirit of antichrist, whereof ye have heard that it should come; and even now already is it in the world." (1 John 4:3)
The four passages in the New Testament that use this term are unique to the apostle John (1 John 2:18, 22; 4:3; and 2 John 1:7).The term itself is a transliteration of the Greek compound word anti plus christos, meaning one who is "against" Christ.
John distinguishes between "the" Antichrist (1 John 2:18) and the "many" antichrists against whom we are continually fighting today.
Although a sincere Christian should be aware of the Antichrist (the "man of sin" in 2 Thessalonians 2:3-10), far more caution is urged to identify and fight the spirit of antichrist that is already here!
To begin with, it should be noted that there is no specific word for "spirit" in 1 John 4:3. The English word is supplied by the translators to clarify the obvious meaning of the text, that it is the attitude or character of antichrist of which we are to be wary. Those who have this spirit are liars (1 John 2:22), mainly because they refuse to accept the truth that Jesus is the Christ.
Further rejection of that truth centers around denial of the incarnation of Christ, that Jesus is the Creator God come in human flesh (1 John 4:3 and 2 John 1:7). Those who would deny that truth embrace the very core of all lies and become anti Christ.
From such as these we are to turn away (2 Timothy 3:5). HMM III