We numerically demonstrate ultra-wideband mid-infrared supercontinuum (SC) generation in a liquid-filled arsenic–selenide circular photonic crystal fiber (C-PCF). The inner ring air-holes are filled with two different nonlinear liquids: chloroform (CHCl₃) and carbon disulfide (CS₂). Based on simulation results, we show that ultra-wideband SC spectra spanning from 1 to 20  μm can be achieved using only 5-mm long CHCl₃ liquid filling with a pump optical pulse of 10-kW peak power at the wavelength of 2.55  μm. In addition, using 5-kW peak power, SC spectrum spanning up to 12  μm is obtained in the case of the CS₂ liquid-filled C-PCF.