Summary: On the basis of the formalism of the fermionic coherent state of K. E. Cahil and R. J. Glauber [Phys. Rev. A 59, No. 2, 1538–1556 (1999)], we have provided an exact solution to a model of a harmonic oscillator coupled to a fermionic environment via a quantum non-demolition type interaction. Quantum phase diffusion and linear entropy dynamics show their signature felt by the suppression of decoherence with temperature in comparison to the bosonic bath case, which may be worth investigating for their application in the coherent dynamics domain at finite temperature. We have shown an unconventional motional narrowing of the quantum Kubo oscillator, which is realized from this model due to the antibunching character of fermionic quantum noise. It is possible to bring this out explicitly here by the consideration of the non-commutative property of interaction obeying the Grassmann algebra.