Yes, it's possible. Orgasm and ejaculation are two separate processes, so one can occur without the other. However, more often than not, they happen at the same time. Orgasm is the release of sexual tension that has built to a peak -- although intensity can vary with each encounter depending on physical or psychological factors. It includes an increase in heart rate, a surge in blood pressure, involuntary muscle contractions in the genitals and spasms in the arms, legs or other areas of his body. In contrast, ejaculation is the expulsion of semen from the tip of the penis. Some men who can orgasm without ejaculating have perfected the art of flexing their pubococcygeal (PC) muscle during sex, but before ejaculatory inevitability (the point of no return). This can prevent the fluid from being released. Men can learn to isolate this muscle, which is located in the pelvic area, by stopping urination midstream, and they can strengthen it over time with repeated tightening and releasing exercises. A guy who orgasms without ejaculating could also be experiencing retrograde ejaculation, which causes the fluid to flow backward into the bladder, rather than forward through the urethral opening, and can be detected by cloudy urine post-ejaculation. While it's most common in men with diabetes, multiple sclerosis or those who have had prostate surgery, it's best to go to a doctor for a proper diagnosis if symptoms occur.
One word of warning: This is not a reliable form of birth control, so always use protection.