Nanocrystalline Zn1-xMnxO (0.005 <= x <= 0.02) shows room temperature ferromagnetic behaviour. The electron spin resonance spectra of Zn1-xMnxO (0.005 <= x <= 0.02) consist of a broad resonance line stemming from interacting spins and a set of hyperfine structure lines originating in the presence of the paramagnetic Mn2+ ions. The broad resonance lines and the observation of resonance at low field indicate the magnetic inhomogeneity of the sample. The ferromagnetic contribution coming from the cationic interaction like Zn2+-Zn2+, Zn2+-Mn2+ independently or through oxygen vacancies dominate over the paramagnetic behaviour of Mn2+-Mn2+ interaction and gives rise to ferromagnetic behaviour in Mn doped ZnO system. (C) 2018 Elsevier B.V. All rights reserved.