NATO's Article 6 of the Treaty states:

"an armed attack on one or more of the Parties is deemed to include an armed attack: on the territory of any of the Parties in Europe or North America, on the Algerian Departments of France, on the territory of or on the Islands under the jurisdiction of any of the Parties in the North Atlantic area north of the Tropic of Cancer"

With Goa located under the Tropic of Cancer NATO was under no obligation to defend Portugal during the Indian invasion of Goa, although there were political condemnation from many NATO members such as the US and the Netherlands. At the time the Soviet Union was a major supporter of India (fun fact Brezhnev was in India when it happened and applauded India for their actions). On top of this the Soviets vetoed an official UN condemnation of the annexation.