The disposal of a capital asset in Australia, in the course of carrying on your business, is a taxable sale and you are required to account for GST on that sale. This applies even if the asset was purchased before 1 July 2000 or the asset is sold to an individual who is not in business (a private sale).

https://www.ato.gov.au/Business/GST/In-detail/Rules-for-specific-transactions/Business-asset-transactions/GST-and-the-disposal-of-capital-assets/