A significant difference in residual feed intake (RFI, −1.02 vs. 1.02 kg of DM) measured under grazing conditions in beef heifers carrying different genetic marker (presence – V group or absence – C group of 3 allelic variants of the genes neuropeptide Y (NPY), IGF-1 and leptin) was reported. The objective of this study was to explore if grazing activities would be associated with the RFI measured in 2 beef cattle groups: carrying the genetic marker associated with low RFI or not carrying the genetic marker. Grazing activities were measured in beef heifers (370 ± 28 d, 294 ± 37.4 kg of BW, n = 18) grazed on unrestricted and high quality temperate pasture. Grazing activities (grazing, ruminating and idling) were determined using behavior recorders in 2 sequential moments (wk 4 and wk 5) during herbage dry matter intake (DMI) determinations. Intake rate was obtained as the ratio between herbage DMI and actual grazing time of each animal. Data were analyzed as repeated measures. The model included genetic marker group (V or C), week and their interaction as fixed effects and paddock as random effect. More efficient heifers under grazing condition (V group) tended (P ≤ 0.14) to spent 45 min less in grazing time and to graze at a lower intake rate than less efficient heifers. Our results suggest that grazing activities would contribute to the biology behind RFI in growing heifers at grazing condition. Further experiments are needed to uncover drivers for better understanding the variation in RFI under grazing condition