This paper explores the problem of the current global financial crisis, using a behavioral perspective. Particularly, the main objective of this paper is to test whether overconfidence bias can explain excessive volatility witnessed during global financial crisis in developed and emerging equity markets. Empirical results of EGARCH estimated models show an asymmetric effect of volatility for all equity market indexes. The relation between excessive trading volume of overconfident investors and excessive prices volatility is then estimated. The results indicate that conditional volatility is positively related to trading volume caused by overconfidence bias. This finding provides strong statistical support to the presence of overconfidence bias among investors in developed and emerging stocks markets. This cognitive bias contributes to the exceptional financial instability that erupted in 2008. However, during the subprime financial crisis period overconfidence bias cannot explain volatility because of the loss of confidence by investors in financial markets.