We have demonstrated the effect of hydrostatic pressure on magnetic and transport properties, and thermal transport properties in electron-doped manganites CaMn_1-xSb_xO_3. The substitution of Sb^5+ ion for Mn ^4+site of the parent matrix causes one-electron doping with the chemical formula CaMn^4+_1-2xMn^3+_xSb^5+_xO_3 accompanied by a monotonous increase in unit cell volume as a function of x. Upon increasing the doping level of Sb, the magnitudes of both electrical resistivity and negative

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... ebeck coefficient are suppressed at high temperatures, indicating the electron doping. Anomalous diamagnetic behaviors at x=0.05 and 0.08 are clearly observed in field cooled dc magnetization. The effect of hydrostatic pressure on dc magnetization is in contrast to the chemical pressure effect due to Sb doping. The dynamical effect of ac magnetic susceptibility measurement points to the formation of the magnetically frustrated clusters such as FM clusters embedded in canted AFM matrix.