If we define the universe as what was caused from Big Bang, it can't be infinite since it hasn't had infinite time to expand. But if we say everything in existence, it's hard to know if there is a center since we don't know what could be beyond our universe from Big Bang (other universes for example).
In our universe from Big Bang, it will appear to anyone that any place within it is the center, but this is because the oldest light is from when the observer was in the Big Bang, which it will receive from all directions, like the cosmic microwave background.