Yes, a Nigerian Senator or Member of the House of Representatives can be removed from office. This also applies to members of State Houses of Assembly. The constitution answers this question in Article 69 which requires that a signed petition is delivered to the INEC Chairman, followed by an INEC organised referendum. The member will be removed if he loses the referendum.
Using an example, let us assume the number of voters registered to vote in a constituency is 100,000.
Firstly, at least 50,001 voters (more than half), must sign a petition and deliver it to the INEC Chairman.
Secondly, the signatures must be verified to ensure that none is fake and all signatories are on the electoral register.
Thirdly, within 90 days of receiving the petition, INEC will conduct a referendum in the member's constituency. If a simple majority vote in favour of removing the representative, then the INEC Chairman will issue a Certificate of Recall to the presiding officer of either of the National Houses of Assembly to remove the representative.
A by-election is then held to elect the next representative, but the previous representative can still run if his or her party supports and nominates them for the election.
This process applies equally to the Senate and the House of Representatives.
While we've established that representatives can be recalled, this process has never succeeded in Nigerian history. Most recently, in Plateau State in 2005, the incumbent Speaker of the Plateau State House of Assembly Solomon Lalong, emerged victorious at a referendum on his mandate.
At the first recorded attempt to recall a Senator, the then Deputy Senate President Ibrahim Mantu, INEC failed to act on the petition within the stipulated 90 days, causing the motion to be dropped. Most recently, Senator Dino Melaye was served a recall petition by INEC.
Find out more about the recall process by reading the following articles.
Premium Times: Dino Melaye; How The recall Process Works