Daniel Mason, who works for William Graham, said he had not "fully understood" the meaning of the speech.
Mr Powell was sacked as shadow defence secretary after his 1968 speech criticising the level of immigration.
In a Facebook post, Mr Mason asked if Mr Powell had been a "mad racist" or a "visionary".  The post was removed.
A Conservative MP for Wolverhampton South West, Mr Powell spoke of his concerns about immigration, claiming that "British" families could lose out on matters such as housing, resulting in racial tension.
Quoting Virgil's Aeneid during a speech in Birmingham, he said: "As I look ahead, I am filled with foreboding. Like the Roman, I seem to see 'the River Tiber foaming with much blood'."
The then Tory leader Edward Heath sacked Mr Powell from his front bench team, telling the BBC: "I believed his speech was inflammatory and liable to damage race relations."
Despite widespread condemnation, the MP said he received about 100,000 letters from ordinary people backing his comments.
Mr Mason had written on Facebook: "Enoch Powell gave a speech 'Rivers of Blood'.. worth reading today.. 'blood on the streets' the rantings of a mad racist? or a visionary?"
He later said: "I want to apologise unreservedly for this Facebook post.
"Ignorance is no excuse but had I fully understood the meaning behind the speech I would never have shared it."
A spokesman for Mr Graham said:  "This misinformed, disappointing and deeply disrespectful post is unacceptable and totally at odds with the views of any right-thinking person.
"Clearly this is a matter for William as the employer and he will be taking appropriate action."
An aide to a Tory AM has apologised for a social media post after the Paris attacks referring to Enoch Powell's notorious "rivers of blood" speech.