Description: Introduction Low back pain (LBP) is a prevalent and costly condition. The majority of patients experiencing LBP are managed in primary care, where first-line care recommendations consist of advice to self-manage and remain active. Internet interventions present a potential means of providing patients with tailored self-management advice and evidence-based support for increasing physical activity. Methods/analysis This protocol describes a single-blind, randomised controlled feasibility trial of an internet intervention developed to support the self-management of LBP in primary care. Patients are being randomised to 1 of 3 groups receiving either usual primary care, usual primary care with the addition of an internet intervention or an internet intervention with physiotherapist telephone support. Patients are followed up at 3 months. Primary outcomes are the feasibility of (1) the trial design/methods, (2) the delivery of the internet intervention and (3) the provision of telephone support by physiotherapists. Secondary outcomes will include exploratory analysis of estimates and variation in clinical outcomes of pain and disability, in order to inform a future main trial. Ethics/dissemination This feasibility trial has undergone ethical scrutiny and been approved by the National Health Service (NHS) Research Ethics Committee, REC Reference 13/SC/0202. The feasibility findings will be disseminated to the research community through presentations at conferences and publication in peer review journals. Broader dissemination will come following a definitive trial. Trial registration number ISRCTN 31034004.