Why is carbon monoxide stable(compare with other flammable gas) in room temperature?
What gives you the impression that carbon monoxide does not burn easily?  

Below I will link to a youtube video of an accidental ignition of a large amount of carbon monoxide.  But be warned!  The video is a highly uncontrolled, dangerous experiment.  The person who performed it did not have appropriate safety equipment and acted very recklessly.  DO NOT TRY TO PERFORM A SIMILAR EXPERIMENT YOURSELF unless you know what you are doing and have


A CO detector / alarm
A buddy in the room with you
A fire extinguisher
Lots of experience synthesizing gases using laboratory apparatus


...



OK, all that said, here is the video.  As you can see, carbon monoxide is quite flammable.  And that guy is an idiot, at least in my book.

The autoignition temperature of $\ce{CO}$ is ~609 &deg;C, only 100 &deg;C or so higher than the $\ce{H2}$ autoignition temperature, and lower than the autoignition temperature for solid carbon. The LEL and UEL are 12.5% and 74%, respectively, which is a very wide range compared to most compounds.  

Compared to other gases, $\ce{CO}$ explosions may be comparatively less violent because of the relatively smaller change in moles during the combustion reaction:

$$\ce{2CO(g) + O2(g) -&gt; 2CO2(g)}$$

Thus, two moles of gas are formed from three moles of reactants, which means that the shock waves and pressure forces produced by a sudden $\ce{CO}$ combustion reaction / explosion are not as large as some gases such as say propane.