Online rumors last week that Leopoldo Lopez, 46, was dead or hospitalized worsened tensions in a country gripped by a deadly political crisis.
The government had responded by releasing a video of Lopez stating the date and affirming that he was alive.
His wife Lilian Tintori said the video was manipulated and insisted on seeing him in person.
She said yesterday that she had finally seen him and quoted him as saying: "I am well, I am alive, I am strong."
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The opposition is demanding elections to replace socialist President Nicolas Maduro, whom they blame for an economic crisis.
Clashes in the protests have left 36 people dead and hundreds injured, according to authorities.
Tintori published a series of messages from Lopez on Twitter.
In them, he called on the opposition to keep up the protests and urged the military to drop their support for Maduro.
The opposition said it plans to march to the headquarters of the education ministry in central Caracas today in the latest street protest.
Lopez was detained in 2014 and sentenced to 14 years in jail for supposedly inciting violence in anti-government protests.
A fugitive prosecutor in the case later cast doubt on Lopez's conviction.