Let $G$ be a locally compact group and $μ$ an admissible probability measure on $G$. Let $(B,ν)$ be the universal topological Poisson $μ$-boundary of $(G,μ)$ and $Π_s(G)$ the universal minimal strongly proximal $G$-flow. This note is inspired by a recent result of Hartman and Kalantar. We show that for a locally compact second countable group $G$ the following conditions are equivalent: (i) the measure $ν$ is the unique $μ$-stationary measure on $B$, (ii) $(B,G) \cong (Π_s(G),G)$.