As in 'This food is not expired' or 'I recently renewed my membership so it is not expired'. A word I could use in place of 'not expired' in both these sentences (so not words like 'edible' or 'valid' which are too specific).
The opposite is simply unexpired. Not used very frequently, but it is a real word.
More common usages are either more specific (e.g. fresh as opposed to expired when talking about food spoiling), or use more words (e.g. still good, which is probably used more often than unexpired to mean the same, but is rather informal).