Flostaøya is an island in Arendal municipality in Agder county, Norway.

The island lies about 11 kilometres (6.8 mi) northeast of the town of Arendal.

Some of the larger villages on the island include Arnevik, Narestø, and Kalvøysund.

[1] The island was historically part of the municipality of Dypvåg until 1902.

[2] The historic Flosta Church is located just north of Narestø on the island of Flostaøya.