  A pair $(C, D)$ of group codes over group algebra $R[G]$ is called a linear
complementary pair (LCP) if $C \oplus D =R[G]$, where $R$ is a finite principal
ideal ring, and $G$ is a finite group. We provide a necessary and sufficient
condition for a pair $(C, D)$ of group codes over group algebra $R[G]$ to be
LCP. Then we prove that if $C$ and $D$ are both group codes over $R[G]$, then
$C$ and $D^{\perp}$ are permutation equivalent.
