You should be counting it, but there are probably at least a couple of ways to count it:
1) As suggested by other people in this thread; determine what the payout would be, when the earliest your payments can start, and base your FIRE number on that information.
2) If you are able to take your portion of contributions toward your pension and roll them into another account upon separating from your employer, you can count that money toward your overall savings.
If you haven't been with your employer very long and don't plan on working very long (by pension standards), your better option may be to just take your contributions and run. But, if, like me, you are relatively young and already have years of service credits toward your pension, then look at the potential monthly payout upon early retirement. Covering the gap between early retirement and a pension beginning at, for example, age 55, can make early retirement that much more viable.