According to the link I have attached below, there are 18 active volcanoes located in the Atlantic Ocean. Not all have been named. Some of the 18 are entirely under water. Like volcanoes found in other areas of the world, they tend to be found where the tectonic plates of the Earth's crust are being pulled apart.
Tristan de Cunha is an island, shield volcano located in the southern Atlantic about midway between the southern tip of Africa and the country of Argentina in South America. A shield volcano is one whose lava has flowed mostly in a low, flat manner, so that it is wide, and not very tall. Tristan de Cunha has several cones and vents. Its last eruption happened in 1961.
Another volcano in the Atlantic that has a name is Ascension Island. It is north of Tristan de Cunha, about halfway between the countries of Brazil (South America) and Angola (Africa). It has many cones and domes, and is the tip of a volcano that rises from the bottom of the ocean, making it a stratovolcano. This type of volcano has lava that is thicker and slower moving than the more liquid type that formed Tristan de Cunha. This is one reason why it rises so high--the lava tends to cool before it has a chance to flow further out and flatten, so it makes a higher cone. It is considered active, although no eruptions have occurred since its discovery on Ascension Day in 1501.
The link I have provided below lists all the active Atlantic volcanoes.