Balance training has been shown to be effective in reducing risks of falling, which is a major concern for older adults. Usually, exercise programs are individually prescribed and monitored by physiotherapeutic or medical experts. Unfortunately, supervision and motivation of older adults during home-based exercises cannot be provided on a large scale, in particular, considering an ageing population. Augmented reality (AR) in combination with virtual coaches could provide a reasonable solution to this challenge. We present a first investigation of the acceptance of an AR coaching system for balance training, which can be performed at home. In a human-centered design approach we developed several mock-ups and prototypes, and evaluated them with 76 older adults. The results suggest that older adults find the system encouraging and stimulating. The virtual coach is perceived as an alive, calm, intelligent, and friendly human. However, usability of the entire AR system showed a significant negative correlation with participants' age.