According to the Scriptures, the "mark of the beast" is received on the right hand or forehead. With modern technology, it is very possible that this mark may be directly linked with a computer chip. But regardless if it is or isn't, everyone who is living immediately before the return of Christ will be forced to take this mark in order to buy or sell anything:
"He also forced everyone, small and great, rich and poor, free and slave, to receive a mark on his right hand or on his forehead so that no one could buy or sell unless he had the mark, which is the name of the beast or the number of his name. This calls for wisdom. If anyone has insight, let him calculate the number of the beast, for it is man's number. His number is 666" (Rev. 13:16-18).
But this mark, which will be universally issued around the entire world, MUST NOT be received under any circumstances, even by Christians! Scripture goes on to say:
"A third angel followed them and said in a loud voice: 'If ANYONE worships the beast and his image and receives his mark on the forehead or on the hand, he, too, will drink of the wine of God's fury, which has been poured full strength into the cup of his wrath. He will be tormented with burning sulfur in the presence of the holy angels and of the Lamb. And the smoke of their torment rises for ever and ever. There is no rest day or night for those who worship the beast and his image, or for anyone who receives the mark of his name. This calls for patient endurance on the part of THE SAINTS who obey God's commandments and remain faithful to Jesus' " (Rev. 14:9-12).
More:
http://www.evangelicaloutreach.org/markbeas.htm