In this paper quadratic sets of a $3$-dimensional locally
projective regular planar space $(\cal S,\cal L,\cal P)$ of order $n$ are
studied and classified. It is proved that if in $(\cal S,\cal L,\cal P)$ there
is a non-degenerate quadratic set $\bf H$, then the planar space is
either $\mathop{\rm{PG}}(3,n)$ or $\mathop{\rm{AG}}(3,n)$. Moreover in the first case $\bf H$
is either an ovoid or an hyperbolic quadric, in the latter case
$\bf H$ is either a cylinder with base an oval or a pair of parallel
planes.