No, they know He is there. Deep down inside they know. Their pride and sin, the darkness in their hearts, won't allow themselves to admit it. But someday they will confess, they will bow down.
Ro 1:
18The wrath of God is being revealed from heaven against all the godlessness and wickedness of men who suppress the truth by their wickedness, 19since what may be known about God is plain to them, because God has made it plain to them. 20For since the creation of the world God's invisible qualities—his eternal power and divine nature—have been clearly seen, being understood from what has been made, so that men are without excuse. 21For although they knew God, they neither glorified him as God nor gave thanks to him, but their thinking became futile and their foolish hearts were darkened. 22Although they claimed to be wise, they became fools 23and exchanged the glory of the immortal God for images made to look like mortal man and birds and animals and reptiles.
atheists often come to God on their deathbed. When they are broken and hopeless and have no-one to turn to, they seek God.