Are protestants capable of mortal sin?

I’m a new Catholic, and most of my family remains protestant. I understand that for a sin to be mortal, it must meet three criteria:

(1) It must be a grave or serious offense.
(2) The person must be aware that it is a grave or serious offense.
(3) The person must willfully commit the offense.

My question is this: since some protestants believe that once they are “saved” they are always saved (ie. nothing will separate them from God), are any of their sins mortal? It seems that they would be unaware that any of their sins would separate them from God.

I’m referring to protestants with valid baptisms, of course.

Yes, all human persons are capable of mortal sin. It is not necessary for someone to have a perfect theological understanding of sin in order to be culpable for sin. The three conditions for mortal sin can be met by any person who has reasonable faculties.

DISCLAIMER: The views and opinions expressed in these forums do not necessarily reflect those of Catholic Answers. For official apologetics resources please visit