In today's world, smartphones are an indispensable part of people's daily lives because smartphones facilitate daily routines. However, problematic or excessive use of smartphones can cause some psychological problems. Nomophobia is considered as one of the psychological problems caused by excessive use of smartphones. Nomophobia is referred to as modern age phobia and refers to irrational fears and anxieties of a person who cannot access or communicate with their mobile phone. Therefore, this study examines the prevalence of nomophobia among college students, behavioral patterns associated with nomophobia, and reveals the relationship between nomophobia and depression-anxiety-stress. A personal questionnaire, the Depression Anxiety Stress (DASS-42) and Nomophobia (NMP-Q) scales were used to investigate the research questions. Descriptive statistics, one-way analysis of variance (ANOVA), independent samples t-test, Pearson correlation coefficient and simple linear regression methods were used to analyze the data. The results show that the level of nomophobia among college students is higher than average. There were significant differences between the level of nomophobia and the college students' behaviors such as carrying a charger, checking the smartphone after waking up, checking the phone frequently during the day, the duration of daily smartphone use, and the time of internet use through the smartphone. A positive correlation was found between nomophobia and depression-anxiety-stress level. Finally, in the regression analysis, the model was found to be statistically significant. This result shows that the level of nomophobia is a significant predictor of the level of depression and anxiety stress. The results obtained show that nomophobia has negative impact on mental health.