Antimicrobial resistance is a major public health concern associated with inappropriate antibiotic use and self-medication. This exploratory study described antibiotic self-medication practices in a convenience sample of adults in Romania by assessing antibiotic-related knowledge, attitudes, and behaviours, identifying sources of antibiotic acquisition, and exploring associations with sociodemographic factors. Data were collected through an online survey (June 2024–September 2025; N = 465). Respondents generally demonstrated good awareness of antimicrobial resistance, although misconceptions about appropriate antibiotic use remained common. Overall, 59.4% correctly recognised that antibiotics are effective only against bacterial infections, while 86.7% were aware that bacteria can become resistant to antibiotics. Antibiotics were predominantly obtained through prescription-based channels, with 97.2% reporting pharmacy dispensing upon presentation of a medical prescription. However, 7.7% reported obtaining antibiotics without a prescription, and 7.1% reported using leftover antibiotics from previous treatments. Among respondents who had used antibiotics during the previous year (n = 298), self-medication prevalence was 22.1% (95% CI: 17.8–27.2%), or 14.2% of the total sample (66/465). Exploratory sociodemographic associations were weak and item-specific. Age was associated with antibiotic treatment frequency and keeping antibiotics at home, whereas educational attainment and gender were associated only with treatment frequency. The results support responsible antibiotic use and control of antibiotic dispensing.