  We study the (2+1)-dimensional Dirac oscillator in the presence of an
external uniform magnetic field ($B$). We show how the change of the strength
of $B$ leads to the existence of a quantum phase transition in the chirality of
the system. A critical value of the strength of the external magnetic field
($B_c$) can be naturally defined in terms of physical parameters of the system.
While for $B=B_c$ the fermion can be considered as a free particle without
defined chirality, for $B<B_c$ ($B>B_c$) the chirality is left (right) and
there exist a net potential acting on the fermion. For the three regimes
defined in the quantum phase transition of chirality, we observe that the
energy spectra for each regime is drastically different. Then, we consider the
$z$-component of the orbital angular momentum as an order parameter that
characterizes the quantum phase transition.
