Yes, we see that in Matthew 7:22-23. I have heard certain individuals state they know someone who was truly saved, but later lost their salvation, yet only God truly knows the heart of individuals. Certain people "on the surface" may do a good job of looking like the real deal for a while (like Judas Iscariot, who was an unbelieving, unclean devil who betrayed Jesus - John 6:64-71; 13:10-11) yet to the other 11 disciples, he looked like the real deal, but Jesus knew his heart. There are genuine Christians and there are "nominal" Christians. There are genuine believers and there are make believers.