Hyperfine induced $2s2p~^3P_0 rightarrow 2s^2~^1S_0$ transition rates in an external magnetic field for Be-like $^{47}$Ti were calculated based on the multiconfiguration Dirac-Fock method. It was found that the transition probability is dependent on the magnetic quantum number $M_F$ of the excited state, even in the weak field. The present investigation clarified that the difference of the hyperfine induced transition rate of Be-like Ti ions between experiment [Schippers {sl et al.}, Phys Rev Lett {bf 98}, (2007) 033001(4)] and theory does not result from the influence of external magnetic field.