The very question exists because God exists. In the absence of God, the one who asks this question would not exist at all.

The answer is Yes. Whoever would draw near to God must believe that He exists and that He rewards those who seek Him. – Heb 11:6. The ungodly and unrighteous men suppress the truth of the existence of God. For what can be known about God is plain to them, because God has shown it to them. For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So, they are without excuse. For although they knew God, they did not honour him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened. – Rom 1:19-21.

The unseen God showed Himself to humans in Jesus Christ.