Olives — Food safety facts
Feed with care · Dogs · full breakdown on the linked food page
Pitted, plain olives occasionally. Brine-cured olives are very salty — rinse first.
Short answer
Yes, that's generally fine. Plain, pitted olives are not toxic to dogs in small amounts like this. Just watch for signs of an upset stomach, such as vomiting or diarrhea, and contact your vet if you see them.