Here is John's take on the Antichrist:
1Jn_2:18 Children, it is the last hour, and as you have heard that antichrist is coming, so now many antichrists have come. Therefore we know that it is the last hour.
1Jn_2:22 Who is the liar but he who denies that Jesus is the Christ? This is the antichrist, he who denies the Father and the Son.
1Jn_4:3 and every spirit that does not confess Jesus is not from God. This is the spirit of the antichrist, which you heard was coming and now is in the world already.
2Jn_1:7 For many deceivers have gone out into the world, those who do not confess the coming of Jesus Christ in the flesh. Such a one is the deceiver and the antichrist.
Add to John's testimony Paul's call to fight the devil now:
Eph 6:10 Finally, be strong in the Lord and in the strength of his might.
Eph 6:11 Put on the whole armor of God, that you may be able to stand against the schemes of the devil.
Eph 6:12 For we do not wrestle against flesh and blood, but against the rulers, against the authorities, against the cosmic powers over this present darkness, against the spiritual forces of evil in the heavenly places.
Eph 6:13 Therefore take up the whole armor of God, that you may be able to withstand in the evil day, and having done all, to stand firm.
Therefore, I draw the conclusion that we must fight Satan and the demons, especially through prayer by claiming Jesus' victory over them, all the time in the present until Jesus comes to banish them:
Eph 6:16 In all circumstances take up the shield of faith, with which you can extinguish all the flaming darts of the evil one;
Eph 6:17 and take the helmet of salvation, and the sword of the Spirit, which is the word of God,
Eph 6:18 praying at all times in the Spirit, with all prayer and supplication. To that end, keep alert with all perseverance, making supplication for all the saints,
Eph 6:19 and also for me, that words may be given to me in opening my mouth boldly to proclaim the mystery of the gospel,
Eph 6:20 for which I am an ambassador in chains, that I may declare it boldly, as I ought to speak.