  The existence of bound states of the system $(\al,e,e,e)$ in a magnetic field
$B$ is studied using the variational method. It is shown that for $B \gtrsim
0.13\,{\rm a.u.}$ this system gets bound with total energy below the one of the
$(\al,e,e)$ system. It manifests the existence of the stable He$^-$ atomic ion.
Its ground state is a spin-doublet $^2(-1)^{+}$ at $0.74\, {\rm a.u.} \gtrsim B
\gtrsim 0.13\, {\rm a.u.}$ and it becomes a spin-quartet $^4(-3)^{+}$ for
larger magnetic fields. For $0.8\, {\rm a.u.} \gtrsim B \gtrsim 0.7\, {\rm
a.u.}$ the He$^-$ ion has two (stable) bound states $^2(-1)^{+}$ and
$^4(-3)^{+}$.
