i have modified login-config.xml,that is why j_security_check was working but not at the ejb method level
<application-policy name="javaee6-app">
<authentication>
<login-module code="org.jboss.security.auth.spi.UsersRolesLoginModule"
flag="required">
<module-option name="usersProperties">props/javaee6-app-users.properties</module-option>
<module-option name="rolesProperties">props/javaee6-app-roles.properties</module-option>
</login-module>
</authentication>
</application-policy>
<application-policy name="javaee6-app">
<authentication>
<login-module code="org.jboss.security.auth.spi.UsersRolesLoginModule"
flag="required">
<module-option name="usersProperties">props/javaee6-app-users.properties</module-option>
<module-option name="rolesProperties">props/javaee6-app-roles.properties</module-option>
</login-module>
</authentication>
</application-policy>