It happens every spring. Ants weak up from winter and are looking for food. There aren't any in the yard. Your house is best source. They usually come from yard through windows or some other hole in the house. When you find them buy a ants killer spray on and around the entry. It would block their road. They may try somewhere else ,just keep blocking. When weather become warmer, ants will have more food at yard, so they wouldn't come to house anymore.
* ps spray outside the house on the wall not inside house.