  In this paper, we study the positive stability of $P$-matrices. We prove that
a $P$-matrix A is positively stable if A is a $Q^2$-matrix and there is at
least one nested sequence of principal submatrices of A each of which is also a
$Q^2$-matrix. This result generalizes the result by Carlson which shows the
positive stability of sign-symmetric $P$-matrices and the result by Tang,
Simsek, Ozdaglar and Acemoglu which shows the positive stability of strictly
row (column) square diagonally dominant for every order of minors $P$-matrices.
