In this paper, a tri-band metamaterial (MTM) loaded compact monopole antenna is proposed. In the first step of design procedure, a rectangular monopole antenna is improved by replacing the corresponding rectangular patch with a ring resonator. As a result, the first obtained operating frequency is decreased from 2.95 to 2.46 GHz. Then, this operating frequency is reduced to 2.02 GHz utilizing an MTM geometry in the antenna structure. The geometry parameters of the proposed antenna are optimized to provide the applicability for 3G, WLAN, and WiMAX applications. The impedance bandwidths of 600, 1080, and 220 MHz are obtained at 2.02–2.62, 3.48–4.56, and 5.12–5.34 GHz, respectively. Moreover, the equivalent circuit of the proposed antenna has been extracted. The proposed equivalent circuit model is validated through a comparison with corresponding simulation results. The proposed antenna is compact, low profile, via-less, and provides easy fabrication. Considering the first resonance frequency, a compactness of 32% is achieved in comparison to the corresponding unloaded monopole antenna.