There are no flags that are completely identical, but there are several that have similar designs and colors: white, black, green, red. None of them have the color sequence green, white, black like the UAE flag. These four colors are considered pan-Arab (colors of Arab unity). Each of the 4 pan-Arab colors represents a particular Arab dynasty or era: black was the color of the flag of the Islamic prophet Muhammad, white was chosen by the Umayyads, green was chosen by the Fatimids, and red was the flag of the Kharijites.
The flags of Western Sahara(1), Jordan(2), and Palestine(3) have a black, white, and green tricolor and a red triangle instead of the red servant on the left.

The flag of Kuwait(4) and the flag of Sudan(5) also consist of pan-Arab colors. And this is their only similarity to the UAE flag, as the color sequence is different, and the rectangle on the left is replaced by a trapezoid and a triangle, respectively.