As per the ATO, being paid for completing online surveys is usually classified as income for tax purposes. It's considered to be similar to "providing services" under the sharing economy where you get paid for doing something such as a ‘task’, even if it isn’t doesn’t necessarily involve traditional work activities that an employee or contractor might be paid for.
Because the amount isn’t considered wages or business income the amounts received from doing online surveys should be declared as "other income" at question 24 on your income tax return.