Hi new_member, welcome to A2K and the Riddles forum. It is good to see these problems, keep them coming.
I think the answer is 1. Because, you can write every number as a power of another number:
6 equals 6^1,
25 equals 5^2,
64 equals 4^3,
81 equals 3^4,
32 equals 2^5.
What comes next? Well, first we took SIX to a power, then FIVE to a power, then FOUR to a power, and so on. So the '*' should be ONE to a power. However, which power? Well, first we took a number to the FIRST power, then to the SECOND power, and so on. So the '*' should be to the power SIX. That makes that '*' should be ONE to the SIXTH power, which is 1x1x1x1x1x1 = 1.