The government ordered a compulsory evacuation of the 10,000 people on Ambae over two months ago, following the eruption of the Manaro Volcano.
Those displaced are anticipating returning to their homes when the government's state of emergency is lifted at the end of the month.
But a NDMO spokesperson Presley Tari said continued minor volcanic activity on the island means they could be at risk.
"It's still a risk for people to live there. We have some few ash coming down again - but the island is getting back green again. There have been a few times of eruptions, minor eruptions."
Presley Tari said the NDMO is awaiting a decision from the government as to when Ambaens can return to the island.