Despite increasing use of social media and the potential benefits for people with social anxiety (SA) disorder, little is known about the online experience of people with SA. Our study aimed to investigate the occurrence of cognitive and behavioral processes during a series of online and off-line Facebook (FB)-based tasks among individuals with high and low levels of SA. Sixty-one undergraduates with low or high SA were asked to use FB in a laboratory setting, to make an FB post, and to imagine three ambiguous FB scenarios. Participants with high SA reported higher anxiety throughout the study with an interaction effect, indicating greater relative increases in anxiety for those with high SA over low SA across tasks. The high SA group were more likely to negatively interpret the ambiguous FB scenarios than the low SA group. They also reported using more safety-seeking behaviors and having more negative thoughts. The findings suggest that the cognitive and behavioral processes that characterize socially anxious face-to-face interaction are also evident in online communication. Suggestions are made for the clinical implications of such findings.