From the museum description:
Wood, raffia fiber, pigment.
Both men and women belonged to the Bwami society, which played political, economic, social, and religious roles among the Lega. Bwami members moved through progressive grades in the society, and this elegant mask is associated with the second highest grade. Its white color symbolizes death, ancestors, and spirits. Rather than performing the mask, Bwami members wore it on the side of their head or displayed it on specially constructed fences.
by _CMDR_