The ALICE Collaboration at the LHC has measured the elliptic flow of muons from heavy-flavour decays at forward rapidity ($2.5 < y < 4$) in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=2.76$~TeV. The elliptic flow, $v_{2}$, defined as the second order coefficient of a Fourier expansion of azimuthal distributions is extracted using scalar product, two- and four-particle cumulants and Lee-Yang zeros methods. The dependence of the $v_{2}$ of muons from heavy-flavour decays on the collision centrality and transverse momentum, $p_{\rm T}$, is studied in $3<p_{\rm T}<10$~GeV/$c$. A positive $v_{2}$ is observed in semi-central collisions (20--40\% centrality class) in $3<p_{\rm T}<5$~GeV/$c$. The results are compared to transport model calculations.