Is the average IQ still 100? IQ tests have been around since Binet invented them in the early 20th century roughly 100 years ago. The point of the test was to measure your mental against your chronological age (hence the quotient) and then multiplied by 100, so that the average person's IQ was supposedly 100.

I have seen several claims (including this one) that IQs have risen steadily at about 3 points per decade since the early 1900s. So roughly 10 decades at 3 points each makes for what today ought to be a 130 point IQ.

Most tests today though, still score you on percentiles based on an average score of 100 points. How can these facts be consistent?
Intelligence Quotient is a relative score, comparing you to the current average. It is not a fixed, raw intelligence score.


  When current IQ tests are developed, the median raw score of the
  norming sample is defined as IQ 100 and scores each standard deviation
  (SD) up or down are defined as 15 IQ points greater or less,[2]
  although this was not always so historically. By this definition,
  approximately two-thirds of the population scores between IQ 85 and IQ
  115, and about 5 percent of the population scores above 125.[3][4]


....


  Raw scores on IQ tests for many populations have been rising at an average rate that scales to three IQ points per decade since the early 20th
  century, a phenomenon called the Flynn effect. 


... 


  Since the early 20th century, raw scores on IQ tests have
  increased in most parts of the world.[45][46][47] When a new version
  of an IQ test is normed, the standard scoring is set so performance at
  the population median results in a score of IQ 100. The phenomenon of
  rising raw score performance means if test-takers are scored by a
  constant standard scoring rule, IQ test scores have been rising at an
  average rate of around three IQ points per decade. This phenomenon was
  named the Flynn effect in the book The Bell Curve after James R.
  Flynn, the author who did the most to bring this phenomenon to the
  attention of psychologists.[48][49]


http://en.wikipedia.org/wiki/Intelligence_quotient

In addition to various IQ tests giving varying scores, each of them is also standardized to the current average intelligence score. So every test can give you a different score.
Put in other words: An old IQ-test will compare you to what was average IQ at the time the test was standardized - which may be lower than todays average.