The phrase "average intelligence" refers to the level of intelligence that most people have. It means having a standard or typical level of smartness compared to others. Full definition
These working dogs have an athletic body, are very resilient in harsh weather conditions and have an above average intelligence level. (thedogsavenue.com)
Remember, one half of the american people are below average intelligence. (religion.blogs.cnn.com)
And my son has above average intelligence for his age and is more than perfectly healthy. (romper.com)