it doesnt happen everyday it happens like l guess oncea week and it doesnt bother me or anything im justcurious to know what is it thats causing it.

It kind of depends on what u mean by palpitations. You should actually check ur pulse when u experience these episodes. If ur heart is going faster (more than 120 beats per minute) & u r not working out--it could mean u have some sort of electrical disturbance in ur heart. If ur heart rate is normal for u (so, check ur pulse when u r not having the palpitations too to know what is normal for you--usually 60-100 beats per minute), it is hard to say what is causing the ''palpitations.'' Either way, it does not sound too serious since u do not have any other symptoms, but u should have ur doctor do an ECG (or EKG) & look at it for electrical disturbances. If nothing pops up in the doctor is office that day, they can order an ''event monitor'' that will do an EKG when u have ur symptoms. It is very good that u r not having any symptoms--concerning signs would be dizziness, light headedness, fingertips turning blue (when u r not cold), lips turning blue.
PS--For years, l ignored the same symptoms in myself (even after l became a doctor), then one day, they went on for an hour & l had to do something about it. The fix was a fairly benign procedure that did not involve any real surgery--just a wire in the blood vessels to my heart. l recommend u NOT ignore ur symptoms & actually see ur doctor--it is impossible to tell what it is without an EKG.

most the time they are not harmful unless they keep happening
however see a doctor if you are worried
also drink plenty of water and eat right
lack of proper vitamins and some medications,caffiene can cause these