  We present SIMP J21543454-1055308, a new L4$\beta$ brown dwarf identified in
the Sondage Infrarouge de Mouvement Propre (SIMP) survey that displays signs of
low gravity in its near-infrared spectrum. Using the Bayesian Analysis for
Nearby Young AssociatioNs II (BANYAN II), we show that it is a candidate member
of the Argus association, albeit with a 21% probability that it is a
contaminant from the field. Measurements of radial velocity and parallax will
be needed to verify its membership. If it is a member of Argus (age 30-50 Myr),
then this object would have a planetary mass of 10 $\pm$ 0.5
$M_{\mathrm{Jup}}$.
