[en] In this paper we report on the synthesis and the structural, electrical, magnetic and thermal analysis for the new material ${\mathrm{Z}\mathrm{r}}_{1-<!--\; ???\; -->x}{\mathrm{N}\mathrm{b}}_x{\mathrm{B}}_2$ (0.01 $⩽<!--\; ???\; -->$ x $⩽<!--\; ???\; -->$ 0.05). A superconducting transition was observed for all x values studied, despite the non-superconducting matrix ZrB₂, which indicates that the superconducting state is induced by the presence of Nb. The results show that the critical temperature increases with Nb content, reaching its maximum (T _c = 8.1 K) for x = 0.04. From the specific heat data we find a Sommerfeld constant of γ = 1.6 mJ molK⁻² and a Debye temperature of ${\mathrm{\theta <!--\; ??\; -->}}_D$ = 615.5 K. Unconventional behaviors are observed in specific heat dependence with temperature and in $H_{\mathrm{c}1}(T)$ diagram. These behaviors are investigated in $C_{\mathrm{e}}/T$ versus T curve, where an upturn appears for $T<<!--\; <\; -->2.3$ K, and in $ln(C_{\mathrm{e}}/\mathrm{\gamma <!--\; ??\; -->}{T}_{\mathrm{c}})$ versus $T_{\mathrm{c}}/T$ dependence, which shows a clear deviation from BCS theory for low temperatures. Also, contrary to the conventional theories we found a positive curvature for temperatures near T _c in the lower critical field, besides an upturn around 2.3 K. We suggest that these behaviors possibly arise from multiband superconductivity in ${\mathrm{Z}\mathrm{r}}_{0.96}{\mathrm{N}\mathrm{b}}_{0.04}{\mathrm{B}}_2$. (paper)