Cashews — Food safety facts
Feed with care · Cats · full breakdown on the linked food page
Not toxic but very high in fat. A couple of plain cashews are fine; salted or chocolate-covered ones are not.
Short answer
No, it's not an emergency; plain cashews are not toxic to cats. They are very high in fat, so only a couple of unsalted nuts are okay as an occasional treat. Watch your cat for any vomiting, diarrhea, or signs of pancreatitis. If any of those appear, give your vet a call.