NDT(Non-Destructive Testing Evaluation) using electromagnetic(EM) properties can be used for evaluation of physical performance in cement-based materials. In this study, a technique for strength evaluation in cement mortar is proposed through the measured EM properties(conductivity and dielectric constant). For this research, cement mortar specimens with 5 W/C ratios are made for evaluation of compressive strength and they are also utilized for tests of EM properties in the range of $0.2{sim}20GHz$ frequency considering exposure condition and curing period. The averaged conductivity and dielectric constant in $5{sim}20GHz$ frequency are reduced to $83{sim}93%$ and $81{sim}87%$, respectively with increasing water to cement ratios. Through the linear regression analysis, relationships between EM properties and results from the compressive strength are obtained, which shows higher correlated factor($0.93{sim}0.94$) in the specimens exposed to room condition. The gradients in dielectric constant for strength results is measured to be higher than those in conductivity by $3.9{sim}5.1$ times. The results from dielectric constant in room condition shows the most efficient relation for evaluation of strength.