Automatic facial expressions recognition using vision is an important subject towards human-robot interaction. Here is proposed a human face focus of attention technique and a facial expressions classier (a Dynamic Bayesian Network) to incorporate in an autonomous mobile agent whose hardware is composed by a robotic platform and a robotic head. The focus of attention technique is based in the symmetry presented by human faces. Using the output of this module the autonomous agent keeps always targeting the human face frontally. To do that, the robot platform performs an arc centred in the human and the robotic head, when necessary, moves synchronized. In the proposed probabilistic classier the information is propagated, from the previous instant, in a low level of the network. Moreover, to recognize facial expressions are used not only positive evidences but also negatives.