Question: "Is it possible for a person to be saved/forgiven after taking the mark of the beast?"
Answer: The mark of the beast is a mark that will be placed on a person’s forehead or right hand in the end times as a sign of allegiance to the Antichrist (Revelation 13:15–18). Further, no one will be allowed to engage in commerce without the mark (Revelation 13:17). It appears that some form of worship of the Antichrist is associated with receiving the mark (Revelation 14:9; 16:2), and those who refuse to worship the image of the beast will be killed (Revelation 13:15).
The question then arises as to whether a person who has received the mark of the beast can be forgiven. The answer to this question seems to be “no.” Revelation 14:10–11, describing the fate of someone who takes the mark of the beast, declares, “He also will drink the wine of God’s wrath, poured full strength into the cup of his anger, and he will be tormented with fire and sulfur in the presence of the holy angels and in the presence of the Lamb. And the smoke of their torment goes up forever and ever, and they have no rest, day or night, these worshipers of the beast and its image, and whoever receives the mark of its name.”
The eternal destiny of those who take the mark of the beast is the lake of fire. Why is taking the mark of the beast a damnable sin against God? Why would God condemn a person to hell for taking the mark of the beast? It would appear that taking the mark of the beast will be a blasphemous act of willful defiance against God. Receiving the mark of the beast is essentially worshiping Satan. Those who take the mark have made the choice to serve Satan rather than obey God and receive Christ as Savior. When people make that decision during the tribulation, God will grant their request to be eternally separated from Him.