Zn0:95Mn0:05O nanoparticles have been prepared using coprecipitation method and annealed at 400 and 800^oC. These samples have been studied by using X-ray diffraction and dc magnetization measurement techniques. The X-ray diffraction patterns reveal the main wurtzite structure for all the samples. Temperature dependent magnetic measurements have shown a hump for the as-prepared and 800^oC-annealed samples without any indication of a ferromagnetic behavior. No hysteresis and coercivity have been observed at room temperature for any of these samples. However, a good hysteresis has been observed for all the samples at lower temperatures (1.5 K). The coercivity and maximum in magnetization (under 50 kOe field) are found to increase sharply for the 400 and 800^oC-annealed samples as compared to the as-prepared sample. We conclude that the significant change in the observed magnetic behavior for the 400 and 800^oC-annealed samples may be due to the presence of the nanocrystalline impurity phase(Zn,Mn)Mn₂O₄.