Antimicrobial resistance is nowadays a global health issue, mainly related to antibiotic overuse and misuse in different sectors. In veterinary medicine, it is essential to understand farmers’ knowledge and awareness of this serious problem in order to minimize it. In Spain, there are virtually no studies on this issue. A cross-sectional online study was carried out among Spanish farmers to identify their knowledge and awareness of antibiotic use and antimicrobial resistance (AMR). Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated, and logistic regression analysis was also performed. 217 farmers took part in the study, and 215 surveys were analyzed. Farmers were mainly men (60%), middle-aged (76.8%), and with more than 15 years of professional experience (41.4%). They worked mostly in extensive systems of production (53.5%), usually with only one species (54%), with ruminants being found in most farms (70.2%). Most participants showed a satisfactory knowledge of this topic, a positive attitude towards reducing the use of antibiotics, and a growing awareness of their importance for public health, although for almost a fifth of them the meaning of AMR is unclear. Respondents were more likely to achieve satisfactory scores if they were between 31 and 45 years (OR = 2.42, p < 0.05) and rearing only ruminant species (OR = 2.51, p < 0.05). Spanish livestock farmers have an acceptable level of knowledge about antibiotics and AMR, although there are still gaps related to the adequate use of these drugs.