Both of my children had only a small handful of words in their vocabularies at 16 months old. Most of the words had specific meanings, though it took a while for us to figure out what they meant. My son, who will be 3 in June, was also active and didn't really begin expanding his vocabulary until he turned two. My daughter is 20 months old and seems to be following the same pattern.
A few months before my son's 2nd birthay I mentioned his lack of vocabulary to his pedatrician. She told me to keep track of any progress he makes before his 2 year check-up, including new words, facial expressions, hand gestures, and understanding simple directions. His check-up was not long after his birthday and I was able to report that he had made positive progress since I last talked to her.
If your son exhibits any of those language skills, he may simply be a "late bloomer" and could soon be talking your ear off. However, if you feel your son isn't making any connections between words and objects and doesn't exhibit any of those language skills I suggest talking to your pediatrician about it so he can be assessed for possible delays or hearing impairments. Good luck!