For all we know it might be - or it might actually be infinite - but the trouble is that we're limited by what we can see / detect, which is in turn limited by the speed of light.

Another commenter asked something like, what if the universe is much bigger than the observable universe, because everything beyond that 'border' has redshifted out of reach - or hasn't reached us yet / never will, because it's moving away faster than the speed of light.