The award-winning actor was in a hospital in Lagos when he passed away on Monday night, according to local media. He was 40 years old.
Ekubo was best known for his roles in the Weekend Getaway and the music video titled Johnny by Yemi Alade in 2013. He had won many awards and accolades for his work in the entertainment industry and humanitarian efforts.
While his family and management are yet to issue a statement, a member of the Nigerian Guild of Editors told the BBC his death had left the association in shock. Tributes have been pouring in from fans and friends in Nigeria's film industry, known as Nollywood.
"Rest in Peace Alex," fellow actor and producer Funke Akindele posted on social media.
The pair had acted together in the 2020 comedy Omo Ghetto - The Saga.
"I tried to reach out. To see you one more time but guess you knew best," she wrote, adding: "You kept telling me you are fine."
"May your kind soul rest in peace Alex. Ore mi like you fondly called me, I will always remember and cherish the good times we shared together."
The late actor's colleague and friend, Godwin Nnadiekwe, called the news of Ekubo's death heart-breaking.
"Nollywood has lost a rare soul, and I'm lost for words, because this wasn't the plan," he wrote on his Instagram.
Filmmaker Lancelot Imasuen - who gave Ekubo his first film role - described his passing as "devastating and unbelievable", Nigeria's Vanguard news site reports.
Ekubo himself had stepped away from social media, with his last post appearing in December 2024, sparking concern for his health.
Born 10 April, 1986 in Nigeria's Rivers State, the actor received a number of accolades for his work.
The Nollywood star made his acting debut in the 2005 production, Sinners in the House.
He graduated with a degree in law from the University of Calabar and broke into stardom in 2010 after competing in the Mr Nigeria competition.
In 2013, he won Best Supporting Actor in the Best of Nollywood Awards for his role as Andre Dikeh in Weekend Getaway.
Ekubo had received nine awards during his career, including Best of Nollywood's Best Actor of the year (2016) and Best Lead Actor (2022).
Nigeria's First Lady gave him a Special Recognition Award in 2018 for his contribution and development of the country's entertainment industry.
In 2020, he was inducted into the UN's Most Influential People of African Descent (MIPAD) under 40, for his efforts in entertainment and social development.
The following year, Ekubo received an honorary doctorate in arts and culture from the Institut Supérieur de Communication et de Gestion in Benin.
"Tonight is very special and dear to my heart because it's coming at quite a time," he said at the time.
His humanitarian work has also been recognised.
In 2021, he was given the Nigerian National Award of Excellence as the Global Social Giving Actor of the year for his charity work, according to his website.
Ekubo was also awarded a Certificate of Excellence from the Sapio Club - a Nigeria-based community proposing solutions to social and national issues - for his contributions, including humanitarian work.
He briefly courted controversy in 2021 when his fiancée, Nigerian-American actress and model Fancy Acholonu, ended their engagement about three months before their wedding.
