Finance literature suggests the use of the Accounting Beta (BACC) as a proxy for the Capital Asset Pricing Model (CAPM) market beta to estimate the cost of equity capital when the stock price is not available. Previous researchers have aimed to achieve this objective by determining the correlation between accounting variables and the market beta. However, the magnitude of the resulting error in this correlation has remained unknown. The current study is an attempt to test the performance of the BACC as a proxy measure for the market risk and to examine the extent of the statistical error in the correlation between these two measures. Our findings indicate that BACC overestimates the market beta by between 20% and 50%. Applying some corrective measures, such as operational earnings scaled by equity, may lessen this difference to a range of 22%–25%; however, it does not eliminate the error. Our output also suggests that the BACC might be biased when used to assess the risk of small firms.