On the condition of strong electron–LO phonon coupling in an asymmetric quantum dot (QD), we study the eigenenergies and eigenfunctions of the ground and the first excited states under an applied electric field by using variational method of Pekar type. This QD system may be used as a two-level qubit. When the electron is in the superposition state of the ground and the first excited states, we obtain the time evolution of the electron probability density, which oscillates in the QD. It is found that due to the presence of the 3-D anisotropic harmonic potentials in the transverse and longitudinal directions of the QD, the electron probability density shows double-peak configuration, whereas there is only one peak if the confinement is 2-D symmetric in the x- and y-directions. The oscillation period is an increasing function of the transverse and longitudinal effective confinement lengths of the QD, and decreases with respect to the electron–phonon coupling strength and the electric field.