We investigate the gravitational wave background produced by magnetars. The statistical properties of these highly magnetized stars were derived by population synthesis methods and assumed to be also representative of extragalactic objects. The adopted ellipticity was calculated from relativistic models using equations of state and assumptions concerning the distribution of currents in the neutron star interior. The maximum amplitude occurs around 1.2 kHz, corresponding to $\Omega_{gw} \sim 10^{-9}$ for a type I superconducting neutron star model. The expected signal is a continuous background that could mask the cosmological contribution produced in the early stage of the Universe.