Agnostic Theism
Agnostic Theism is the philosophy that encompasses both theism and agnosticism. An agnostic theist is one who disavows knowledge of God's existence, but chooses to believe in God in spite of this.
This belief is much less common than Agnostic atheism, perhaps because Occam's Razor provides a persuasive argument that assuming the nonexistence of a thing is the better "default position" to take when one has no other rational means of taking a position on that thing's existence.