  We report on the anomalous magnetization reversal under hydrostatic pressure
in the lightly electron-doped manganite compound
(Ca$_{1-x}$Sr$_{x}$)Mn$_{0.95}$Sb$_{0.05}$O$_{3}$ with its fixed carrier
content. In a weakly magnetic field cooled measurement, diamagnetic
magnetization is observed for $x\leq 15\%$, which changes to positive values
for $x>15\%$. However, on an application of pressure on the samples with
$x=16\%$ and 17$\%$, magnetization reverses sign and diamagnetism is restored.
We present a magnetic phase diagram as a function of Sr concentration, under
both ambient and hydrostatic pressures. To understand better the
thermodynamical properties of this system, we have measured the specific heat
as a function of temperature under a field cooling of 100 Oe. Our data show no
anomalies associated with the temperature dependent magnetization reversal,
indicating the absence of a long-rang magnetic ordering. The $ac$ magnetic
susceptibility measurement points to the existence of magnetic frustration for
the Sr substituted samples exhibiting diamagnetic behavior.
