The IOM said 24 people had been rescued from the boat, which left the beaches of Zawara in northern Libya and sank off the coast of Sfax.
A Tunisian security official told Reuters news agency that the coastguard had recovered a body.
Those who were rescued were aged between 18 and 40 and of various nationalities, including people from Bangladesh, Egypt, Morocco and Cameroon, Sfax courts spokesman Mourad Turki said.
He added that the initial numbers of those missing were provisional and could rise.
IOM spokesperson Esma Rihane said that the Tunisian navy was continuing to search the area for the missing.
The boat reportedly departed on Sunday night from Zuwara in northern Libya.
Zuwara serves as a departure point for migrants from Libya attempting to reach the Italian coast by sea.
The central Mediterranean, connecting Libya to Italy or Malta, is the most dangerous migration route in the world, the IOM says.
Last July, 43 migrants went missing after a boat carrying 127people from Zuwara sank off Zarzis, a port in southern Tunisia.
The UN agency estimates that more than 1,500 people died or went missing in the area in 2021 and more than 500 so far in 2022.
In recent months, dozens of people have drowned off the Tunisian coast.
Figures from the UN High Commissioner for Refugees (UNHCR) showed that more than 123,000 migrants arrived in Italy in 2021, compared to more than 95,000 in 2020.
THANK YOU SKY NEWS FOR THE ARTICLE
Contribute to your future, a Non Profit Organization and buy us a Coffee with 3 simple clicks and a minute of your time. Imagine what we can do together.
To thank you, we will call you personally.
This is the amount that will be distributed amongst the current shareholders.
Current Share Holders
89/500,000