Heavy flavor production and collectivity in relativistic heavy-ion collisions collisions provide insight into the energy loss mechanism and transport properties of heavy quarks in the QGP medium. In these proceedings, ATLAS measurements on the elliptic flow coefficient, $v_2$, of muons from charm- and bottom-hadron decays in Pb+Pb and $pp$ collisions are presented. Muons with charm and bottom origins are separated based on the transverse impact parameter with respect to the primary collision vertex.The event-plane method is used to extract flow coefficients in Pb+Pb collisions,while a template fit method is used in $pp$ collisions to subtract non-flow contributions using a simultaneous fit to low and high charged-particle multiplicity samples. The extracted $v_2$ coefficients are presented as a function of muon $p_\mathrm{T}$ and event activity.