Background: Fear avoidance behaviour and its association with poor functional outcomes is a well-established phenomenon in musculoskeletal pain. However, there is limited research on fear avoidance in mild traumatic brain injury (mTBI). The current study aimed to expand upon earlier research by exploring the effects of fear avoidance behaviour on outcomes, whilst accounting for factors that may impact recovery in individuals who have sustained a mTBI. Additionally, it investigated potential predictors of individuals who may be at risk of developing fear avoidance behaviour. Methods: One hundred and sixty nine participants (aged 18-69 years) with mTBI were recruited via specialist concussion services throughout the North Island of Aotearoa/New Zealand (NZ). Post-concussion symptoms, fear avoidance behaviour, psychological functioning and functional disability measures were administered at clinic intake (M = 8.74 weeks since injury) and at approximately three-months follow-up (M = 22.91 weeks since injury). Twenty-three participants were lost to follow-up at the three-month time-point. Results: Findings indicate significant predictors for developing fear avoidance behaviour included, a lower level of education and traumatic injury circumstances (assault), with pre-injury mental health history approaching significance (p = .08). Generalised linear modelling found fear avoidance behaviour at clinic intake significantly contributed to both post-concussion symptoms and functional disability at clinic intake and at three-months follow-up, even when factors known to impact these outcomes (e.g., psychological functioning, age, gender) were included in the model. Psychological functioning was also found to contribute to post-concussion symptoms and functional disability. Conclusions: These findings are consistent with previous studies and support an association of fear avoidance with negative outcomes in mTBI. Early identification of the factors that increase the risk of developing fear avoidance will inform implementation of psychological interventions to prevent or modify avoidance behaviour. This has the potential to improve recovery and reduce the personal and societal burden following a mTBI.