It is a matter of doctrine that is often debated. Can someone accept Jesus as payment for their sins at one point in their life, then “lose” that salvation?
I think there is a problem with the whole question. Often you hear it asked, “When were you saved?” I think there can only be 2 answers to that question, and neither one is one anyone can remember. Either you are saved at the cross when Jesus paid the price for your errors, or you are ultimately saved before the throne. Salvation here in our lives is not a “point event,” it must be worked out (Phil 2:12).
A perfect example of this is Simon the Sorceror. It says right in scripture that he believed and was baptized. However, later Peter clearly implies that he is “perishing” and that he needs to repent that God might perhaps forgive him. His salvation was not worked out.
Salvation is a way of life. We need to renew ourselves daily. We can be secure in our faith, but not with our walk.