We deal with the following fractional Schrödinger-Poisson equation with magnetic fieldA is the fractional magnetic Laplacian, V : R 3 → R is a positive continuous potential, A : R 3 → R 3 is a smooth magnetic potential and f : R → R is a subcritical nonlinearity. Under a local condition on the potential V , we study the multiplicity and concentration of nontrivial solutions as ε → 0. In particular, we relate the number of nontrivial solutions with the topology of the set where the potential V attains its minimum.2010 Mathematics Subject Classification. 35A15, 35R11, 35S05, 58E05.