Yanukovych left work last week due to an acute respiratory infection, but said he is now feeling better, Voice of America reported.
His comments came Sunday when 30,000 anti-government demonstrators protested against Yanukovych in Kiev's Independence Square.
Opposition leaders called on citizens to take national flags to the streets for a noon protest Monday, the Kiev Post reported.
"Don't be afraid -- you're Ukrainian," leader Vitali Klitschko said. "Take the national flag with you. We need to show them we're not afraid. There are millions of us."
Yanukovych has accepted the resignation of the prime minister and revoked anti-protest laws in an attempt to ease the tension, but protesters have only demanded more concessions and his resignation.
The protests began in November when Yanukovych turned down an agreement with the European Union.
The United States has supported the protests.