Issue was also reported in the forums here:
During deploying application on Liferay 6.2 (JBoss only!), I see following error in logs:
com.liferay.faces.bridge.logging.LoggerFactory (WARN): Possibly an incompatible version of log4j.jar in the classpath: Could not initialize class org.apache.log4j.LogManager
This warning is misleading when running on JBoss because it does not help the developer know what to do in order to resolve the problem. First it should go to System.out as an INFO message and not to System.err as a WARN message. Secondly, the INFO message should instruct the developer to add WEB-INF/log4j.jar to the WAR deployment in order to get Log4J logging to work. Thirdly, the message is happening on the creation of every logger, when it should only happen once at startup.