Guided Internet-based cognitive-behavioural self-help (ICBT) has been proven to be effective for social anxiety disorder (SAD) by several independent research groups. However, as the proportion of clinical significant change has room for improvement, new treatments should be developed and investigated. A novel treatment is attention bias modification (ABM). This study aimed at evaluating the combination of ABM and ICBT. We compared two groups, one group receiving ICBT and ABM targeting attentional avoidance and the other group receiving ICBT and control training. ABM and control training tasks were both based on the dot-probe paradigm. A total of 133 participants, diagnosed with SAD, were randomised to these two groups. The attention training group (N = 66) received 2 weeks of daily attention training followed by 9 weeks of ICBT. The control group (N = 67) received 2 weeks of daily control training, also followed by 9 weeks of ICBT. Social anxiety measures as well as the attention bias were assessed at pre-assessment, at week 2, and at post-treatment. Results showed no significant differences between the attention training group and the control group. Both groups improved substantially on social anxiety symptoms from pre- to post-assessment (dwithin = 1.39-1.41), but showed no change in attention processes (dwithin = 0.10-0.17). In this trial, the attention modification training failed to induce differential change in attention bias. Results demonstrate that the applied ABM procedure with its focus on the reduction of attentional avoidance was ineffective in the Internet-based setting. The results do not suggest that adding ABM targeting attentional avoidance to ICBT results in better outcomes than ICBT alone.