The Survey of Income and Housing (SIH) from the Australian Bureau of Statistics has data on this, and how it's changed over time. Among their key findings:
In real terms, the average equivalised disposable household income in 2013–14 was $998 per week.
On that site, if you go to Downloads, Data Cube 1 "Household Income and Income Distribution", tab to Table 1.3, and scroll down to Number of Persons x Equivalised disposable household income per week, you can select select some cells to total. Since I'm getting the average from 2013-14 (latest available), I'll use that same column, and choose the rows corresponding to income higher than that average ($1K and up; shifting $2 to align with the category boundary in the data). Summing the cells that are in both that column and those rows, and noting the units is thousands of people, I find that 8,399,300 people earn more than the average in Australia. Rounding up slightly to account for the people who might have been cut off by the slight shift in category boundary and give a number of significant digits which might better reflect answer precision, I'd say 8.4 million people, or 37%.