Involved in the biosynthesis of the arabinogalactan (AG) region of the mycolylarabinogalactan-peptidoglycan (mAGP) complex, an essential component of the cell wall. Catalyzes the transfer of arabinofuranosyl (Araf) residues from the sugar donor decaprenyl-phospho-arabinose (DPA) to the arabinan domain to form terminal beta-(1->2)-linked Araf residues, which marks the end point for AG arabinan biosynthesis before decoration with mycolic acids. Cell wall biogenesis; cell wall polysaccharide biosynthesis. Cells lacking this gene show an absence of the cell wall-bound corynomycolic acids and of beta-(1->2) Araf linkage. Belongs to the AftB family.