Found a couple of these in outlet boxes in a bedroom of house. Is that ok to leave this way? Really not wanting to tear out plaster, if possible. Thank you all.
If they are safely capped off, it's technically fine - though the better option would be to find the other end of them and disconnect and cap off there (so it's just a dead wire for possible future use, ideally also labeled as to where it goes) rather than leave it live but unused.
If you are not actually "abandoning" the wire you don't have to remove all accessible parts, much less rip walls open to remove it (which is never required. Removing accessible parts is, if abandoning.)
Since there might conceivably be use for the wire in the future, just isolate and label. But definitely better to have it isolated if it's disused.