The stability of the [OH,Ps], [CH,Ps] and [NH2,Ps] complexes, where Ps = (e(+),e(-)), have been studied using Monte Carlo techniques and explicitly correlated trial wave functions. For these systems we have computed the ground state energy values using both variational Monte Carlo and fixed node diffusion Monte Carlo methods. Diffusion Monte Carlo results allow us to predict [OH,Ps] and [CH,Ps] systems to be stable against positron and Positronium (Ps) loss. As far as [NH2,Ps] is concerned, its small value of the Binding Energy (BE) does not allow us to conclude about its stability : this is discussed qualitatively including zero point motion of the atoms in the complex.