The most common and most likely answer to this crossword clue is the 4 plus 2 plus 1 plus 3 letter word BUSY AS A BEE
B
U
S
Y
A
S
A
B
E
E
More clues leading to the result BUSY AS A BEE
Buddy explains!
The straight part
We know that "Characteristic of a hive of activity?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case characteristic of a hive of activity? = busy as a bee.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.