Arrieta is a town and municipality located in the province of Biscay, in the Basque Country, Spain. Arrieta is part of the comarca of Mungialdea…Arrieta is a town and municipality located in the province of Biscay, in the Basque Country, Spain. Arrieta is part of the comarca of Mungialdea. It had a population of 552 inhabitants as of 2007, and a population of 564 inhabitants as of 2017.