  The purpose of this paper is to study quasinormal modes (QNM) of a regular
black hole with a cosmological constant due to scalar perturbations. A detailed
study of the QNM frequencies for the massless scalar field were done by varying
the parameters of the theory such as the mass, magnetic charge, cosmological
constant, and the spherical harmonic index. We have employed the sixth order
WKB approximation to compute the QNM frequencies. We have also proved
analytically that the $l=0$ mode for the massless field reach a constant value
at late times. We have approximated the near-extreme regular-de Sitter black
hole potential with the P$\ddot{o}$schl-Teller potential to obtain exact
frequencies. The null geodesics of the regular-de Sitter black hole is employed
to describe the QNM frequencies at the eikonal limit ($ l >>1$).
