  We report simultaneous multicolor near-infrared (NIR) observations of the
supernova associated with x-ray Flash 060218 during the first 16 days after the
high energy event. We find that the light curve rises and peaks relatively fast
compared to other SN Ic, with the characteristic broad NIR peak seen in all
three bands. We find that the rise profile before the peak is largely
independent of NIR wavelength, each band appearing to transition into a plateau
phase around day 10--13. Since the light curve is in the plateau phase when our
observations end at day 16, we can only place limits on the peak absolute
magnitudes, but we estimate that SN 2006aj is one of the lowest NIR luminosity
XRF/GRB associated SNe observed to date. The broad peaks observed in the {\em
JHK$_s$} bands point to a large increase in the NIR contribution of the total
flux output from days 10--16. This evolution can be seen in the broad color and
SED diagrams constructed using {\em UBVRIJHK$_s$} monochromatic flux
measurements for the first 16 days of the event. Ultimately, a 10-day rise time
would make SN 2006aj an extremely fast rise SN Ic event, faster than SN 1998bw
and SN 2003dh, which combined with its underluminous nature, indicates a lower
amount of $^{56}$Ni ejected by the progenitor compared to other XRF/GRB-SNe.
Furthermore, the lack of significant color change during the rise portion of
the burst points to little or no spectral evolution over the first 10 days of
activity in the NIR.
