  We explicitly construct non-tempered cusp forms on the orthogonal group
O(1,5) of signature (1+,5-). Given a definite quaternion algebra B over
$\mathbb{Q}$, the orthogonal group is attached to the indefinite quadratic
space of rank 6 with the anisotropic part defined by the reduced norm of B. Our
construction can be viewed as a generalization of [22] to the case of any
definite quaternion algebras, for which we note that [22] takes up the case
where the discriminant of B is two. Unlike [22] the method of the construction
is to consider the theta lifting from Maass cusp forms to O(1,5), following the
formulation by Borcherds. The cuspidal representations generated by our cusp
forms are studied in detail. We determine all local components of the cuspidal
representations and show that our cusp forms are CAP forms.
