Armin Aleksander Öpik (24 June 1898, in Kunda – 15 January 1983, in Canberra) was an Estonian paleontologist who spent the second half of his career (from 1948) at the Bureau of Mineral Resources in Australia.

His oldest brother Paul Öpik, later a director of the Bank of Estonia, introduced Armin to fossils.

Öpik is mostly known for his work on the Cambrian and Lower Ordovician stratigraphy and paleontology of northern Australia.

Öpik's published on stratigraphic correlation, facies distribution, paleogeography and biostratonomy of the Cambrian and lower Ordovician in Estonia.

When the Russian army threatened to overrun his country of birth in 1944, Öpik fled with his family.

The Silurian crinoid genus Oepikicrinus Ausich, Wilson & Toom, 2019 is named in his honour.