Uncomment this line (remove the '<!--' and '-->')in your log4j.xml file and change the priority value to reflect the output level you want to see:
<category name="org.jbpm"><priority value="INFO"/></category>
Allowable output levels can be found at http://logging.apache.org/log4j/docs/api/org/apache/log4j/Level.html
Thanks for help!
If one else has got the problem, in my case the config file was named log4j.properties.