A reaction-diffusion problem with an obstacle potential is considered in a bounded domain of $R^N$. Under the assumption that the obstacle $K$ is a closed convex and bounded subset of $mathbb{R}^n$ with smooth boundary or it is a closed $n$-dimensional simplex, we prove that the long-time behavior of the solution semigroup associated with this problem can be described in terms of an exponential attractor. In particular, the latter means that the fractal dimension of the associated global attractor is also finite.