If you believed in Jesus, but then stop believing in Jesus.
James 2:19 (NIV), which says: “You believe that there is one God. Good! Even the demons believe that—and shudder.”
Matthew 7:21-23 (NIV):
“Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only the one who does the will of my Father who is in heaven. Many will say to me on that day, ‘Lord, Lord, did we not prophesy in your name and in your name drive out demons and in your name perform many miracles?’ Then I will tell them plainly, ‘I never knew you. Away from me, you evildoers!’”
The Bible verses seem to suggest that you lose your salvation if you’re not doing the will of god. However, I learned that the Bible usually does not mean what it says, rather it means exactly what you wanted to mean.