Former interior minister Yury Lutsenko was detained on Sunday by at least 10 Alpha special security officers while taking his dog out for a walk, his spokeswoman Inna Kysil said.
The former Orange Revolution leader was being held by the Security Service of Ukraine (SBU), an offshoot of the Soviet-era KGB, the spokeswoman said.
The prosecutor general's office confirmed that Lutsenko had been arrested but said that a formal statement would only be issued on Monday.
Last month, officials charged Lutsenko, 46, with abuse of power and taking personal possession of state property.
Ukrainian media reports said the charges are linked to an allegedly improper 40,000-hryvnia (3,840 euros/5,300 dollars) payment the former minister made to his driver.
Lutsenko, who along with Tymoshenko was one of the leaders of 2004 protest movement that briefly deposed the country's current President Viktor Yanukovych, has called the charges against him politically motivated.
A veteran politician, he has held various positions in Ukraine, serving as interior minister in Tymoshenko's government for three years.
Tymoshenko has herself been charged with embezzling 960,000 hryvnias as well as abuse of power and ordered not to leave Kiev.
The charges could put the charismatic Orange Revolution leader in jail for up to a decade and keep her out of politics for three years upon her release.
In February, Tymoshenko lost a hard-fought presidential election battle to Yanukovych, leading her to step down as prime minister in early March and go into opposition.
Since then she has accused Yanukovych of repeated attempts to silence her and sharply criticized his policies, particularly his efforts to build closer ties with Moscow.
A number of former cabinet ministers have been arrested or charged with various crimes since Yanukovych's return to power.
These include former first deputy justice minister Yevhen Korniychuk, the former first deputy justice minister who was arrested this month, and Bogdan Danylychyn, the former economy minister who remains under arrest in the Czech Republic, where he is seeking political asylum.