Is it ok to eat expired yeast?

If you are using the yeast in bread, then if it is expired it may be dead and your bread will not rise. You could make a sponge of the yeast by mixing it with warm (not hot) water and wheat flour; if the sponge becomes foamy, your yeast is fine to use. If you are eating it as a dietary supplement it depends on the form. If it is in a dry form, it probably is okay if it is slightly expired. If it is in a wet form, if the yeast is dead then harmful organisms may replace it and it should probably be discarded.