According to one embodiment, provided is an active material including monoclinic niobium titanium composite oxide particles, and carbon fibers with which at least a part of surfaces of the monoclinic niobium titanium composite oxide particles is covered. The monoclinic niobium titanium composite oxide particles satisfy 1.5≤(α/β)≤2.5. The monoclinic niobium titanium composite oxide particles have an average primary particle size of 0.05 μm to 2 μm. The carbon fibers contain one or more metal elements selected from the group consisting of Fe, Co and Ni, and satisfy 1/10000≤(γ/σ)≤ 1/100. The carbon fibers have an average fiber diameter in the range of 5 nm to 100 nm.