Interannual variability of the Northern Hemisphere (NH) wave energy is diagnosed using 30-year reanalysis data. Particular attention is paid to a relationship between the stationary and transient wave energy in the extratropics. In the NH, the stationary wave energy is negatively correlated with the transient wave energy on interannual timescales. The correlation coefficient is significantly high during mid-winter and spring between the subtropics and midlatitudes. Throughout the year, negative correlation is also found between NH-mean generation rates of the stationary and transient wave energy, which results from the upward Eliassen-Palm flux. This suggests an essential role of the poleward eddy heat flux in the negative correlation of the wave energy. Standard deviation analysis shows that, in the NH, the interannual variability of the total wave energy is primarily explained by the stationary component. These facts provide a useful implication for understanding future projections of the NH extratropical wave activity.