Simply, no.
———————————————————————
a. G-d is the reason for theism. [Here the term god is used loosely, and does not refer only to the Christian god.]
b. G-d is a deity. To quote chutterhanban, and therefore quote G-d, he has said “I Am”.
———————————————————————
“Atheism, as an explicit position, can be either the affirmation of the nonexistence of gods, or the rejection of theism.”— Wikipedia
“Theism, in its most inclusive usage, is the belief in at least one deity.”— Wikipedia
“A deity is a postulated preternatural or supernatural being, who is always of significant power, worshipped, thought holy, divine, or sacred, held in high regard, or respected by human beings.”—Wikipedia
———————————————————————
a. If G-d affirms the nonexistence of gods, he cannot Be. [atheism]
b. If G-d rejects theism, he rejects his belief in at least one deity. [rejection of theism]
c. If G-d rejects his belief in at least one deity, he cannot Be. [rejection of theistic deity]
———————————————————————
If you follow this postulate, and you agree with the definitions of atheism, theism, and deity as presented above, you will agree that it is not possible for G-d to be atheist.