The BSE benchmark index Sensex fell by 131 points in early trade today on selling by funds amid a mixed trend in the Asian region. The 30-share barometer, which had gained 55 points in the previous session, fell by 131 points to 18,644 in the first few minutes of trading led by banking, information technology and oil and gas sector stocks.Similarly, the wide-based National Stock Exchange index Nifty declined by 36 points to 5,632.Brokers said selling by funds amid a mixed trend on Asian bourses mainly influenced the trading sentiment In the Asian region, Hong Kong's Hang Seng index fell by 1.18 per cent, while Japan's Nikkei Index edged was up by 1.42 per cent in early trade.