Is Granite a safe material to use as a flooring in my room?

Granite would not pose a risk to your health because of uranium. You are for more likely to suffer an injury from granite flooring by a slip and fall. Granite is quite hard and could cause serious injury if you fell on it. Also, if you install it yourself you could drop a piece or a box on your foot. That is a much greater threat to your safety than in radiation emited from the stone.