The aim of this study was to develop an innovative method for measuring the activity level of pigs in a barn in real time. An infrared-sensitive camera was placed over two pens of the piggery, images were recorded for 24 h a day for eight days during the fattening period, and the activity and occupation indices were calculated every second in real time using software. In the laboratory, the recorded images were visually labelled to score the animals’ behaviour adopting the Martin and Bateson’s Scan sampling method, and to find a relation with the automatically measured activity index. Pigs’ behaviour was assigned in the following way, 0 - no activity, 1 - fighting or struggling, 2 - biting one another, 3 - abnormal behaviour as nuzzling or suckling one another (interacting pigs), 4 - feed assumption time. Pigs spent most of the time lying inactively (82–90% of the time), following a diurnal rhythm with peaks related to the feeding administration routine; fighting episodes occurred very rarely (0.05–0.10% of the time). Based on the analysis of the automatically measured group activity index compared to the manual labelling, a relation was found between the activity index and the behaviour types (no activity, nuzzling and feeding). The novelty presented in this study was the development of on-line tools to monitor farm animals continuously during their life, in a fully automatic way, with objective measures and criteria without imposing additional stress to the animals.