The café inside The Braid arts centre on Castle Street is the most pleasant daytime option in central Ballymena — a calm, airy space in the ground floor of the town hall building, with decent coffee and a short menu of sandwiches, soups, and baked goods. It's a useful stop before or after visiting the museum, or simply as a place to sit down in the middle of a day in town.
Hours follow the arts centre's opening times, so it's closed in the evenings and on days when The Braid is shut. Worth checking ahead if you're planning around it.