If the jar has an expiration date on it then I would say yes. If there is no date on it then mix it before you use it. Some of the contents can separate if left sitting long enough.
Can A Jar Of Relaxer Expire?
I wouldn't use it if it's out of date, what if it got stronger and your hair fell out, or it got weaker and didn't work at all? I wouldn't bother with it, go and buy some new and fresh.